physics praxis questions 2
Which law explains pressure dependence on temperature under constant volume (isochoric process)? Avogadro's law Gay-Lussac's law Charles's law Newton's law
Explanation: Correct answer: Charles's law According to this law pressure of constant amount of gas, at constant volume increases linear with increasing temperature. This dependence is graphically represented with straight vertical lines, named isochors
Which circuit does not show harmonic oscillation of either the charge or voltage? The LC circuit The RC circuit The Parallel RLC circuit The Series RLC circuit
Explanation: An RC circuit does not show harmonic oscillation. A series RLC and parallel RLC circuit show a change in charge and voltage respectively; and an LC circuit is a simplified RLC circuit in which resistance is assumed to be zero.
If an RC circuit is connected with a resistance R= 10 KΩ and capacitor C= 100 μF, what will be the value of its time constant τ? τ = 1 s τ = 6 s τ = 0 s τ = 10 s
Explanation: Correct Answer τ = 1 s Time constant of this RC circuit will be τ = 1 s as τ = RC = 10 KΩ x 100 μF = 1 s
Only 10% of the energy consumed by a 100 watt filament lamp is converted into light energy. What would be the velocity of an 800 Kg car if all the wasted energy in 1 hour was used to push it? 100 Km/hr 25 ms-1 102.5 Km/hr 90 Km/hr
Explanation: Correct Answer 102.5Km/hr Energy wasted in 1hr = The velocity of 800Kg car with 324000J energy:
Why does a plastic rod have a negative charge after being rubbed with a piece of fur? A.The fur gives up protons to the rod. B.The rod gives up electrons to the air. C.The fur gains protons from the rod. D.The rod gains electrons from the fur.
Answer: D - The rod gains electrons from the fur.
Identify the chemical that has been banned due to the destruction of the ozone layer. Chlorofluorocarbons Ethanol Methylhexabromide Methyl alcohol
Chlorofluorocarbons (CFC's) are chemicals which find their way to the stratosphere without being destroyed in the troposphere due to their low reactivity. Once in the stratosphere, the Cl and Br atoms are liberated from the parent compounds by the action of ultraviolet light. The Cl and Br atoms can then destroy ozone molecules through a variety of catalytic cycles. In 1987, representatives from 43 nations signed the Montreal Protocol to phase out the use of CFC's.
he frequency of a spring with a mass of 1kg is 1Hz. If the mass is replaced by one of 2kg, what is the frequency? 2 Hz 2√2 Hz √2 Hz (1/√2) Hz
Correct Answer: (1/√2) Hz Explanation: Frequency ν= (1/2π)√(k/m) =1. Thus k=(2π)2 . When m is replaced by 2kg, ν= (1/2π)√(k/m)= (1/2π)√(4π2/2)= (2π/2π)√(1/2)= 1/√2. The frequency therefore, is (1/√2) Hz.
An eye specialist prescribes spectacles with a combination of a convex lens of focal length 40 cm in contact with a concave lens of focal length 25 cm. What is the power of that lens combination? +1.5 D -1.5 D +6.67 D -6.67 D
Correct Answer: -1.5 D Explanation: The power of the lens combination is P=P1+P2= 1/f1+1/f2 = 1/0.4+1/(-0.25) = -1.5m-1 = -1.5 D.
If the temperature of the cold reservoir is Tc and the temperature of the hot reservoir is Th, what is the maximum efficiency of an operating heat engine? 1- Tc / Th 1-Th / Tc Tc / Th Tc / Th +1
Correct Answer: 1- Tc / Th Explanation: Carnot's theorem formally states that: No engine operating between two heat reservoirs can be more efficient than a Carnot engine operating between those same reservoirs. The efficiency of a Carnot engine operating between a cold and a hot reservoir with temperatures Tc and Th respectively is 1- Tc / Th.
What is the electric constant ε0 equal to? μ0c02 1/(μ0c0) 1/(μ0c02) μ0c0
Correct Answer: 1/(μ0c02) Explanation: The electric constant ε0 equal to 1/(μ0c02), in which μ0, or the magnetic constant has the defined value 4π × 10−7 H m−1, and c0, which is the speed of light in vacuum, has the defined value 299792458 m s−1.
The Series RLC circuit in the figure is connected to a variable frequency 200V source. L=5H, C=80 μF and R=40Ω. What is the rms potential drop across the resistor at resonance? 100/√2 V 100 V 200/√2 V 200 V
Correct Answer: 200 V Explanation: The rms potential drop across the resistor is Irms x R= 5 x 40= 200V.
A tsunami has a wavelength of 100 km and the water depth is 4000 m. ( g = 10 m/s2) What is the speed of a tsunami in the open ocean? 100 m/s 200 m/s 2000 m/s 5000 m/s
Correct Answer: 200 m/s Explanation: The tsunamis wavelength is much greater than the ocean depth, so it travels as a shallow water wave. In shallow water, wave speed depends only on the water depth, v = √(gh) = √(10 m/s * 4000 m) = 200 m/s ... about the speed of a jet plane
In an AC's main power supply the root mean square voltage is 230V and the frequency is 60 hertz. What is the approximate amplitude of the peak voltage? Assume √2= 1.414
Correct Answer: 325V Explanation: The peak voltage amplitude is equal to √2 Vrms. Here Vrms=230V, therefore Vpeak= √2 Vrms = 1.414 x 230 ≈ 325V . The peak voltage amplitude calculation is not dependent on the frequency.
What can be used to make a low-pass filter? A capacitor A capacitor and resistor in parallel A capacitor and resistor in series Two capacitors in parallel
Correct Answer: A capacitor and resistor in series Explanation: A capacitor and a resistor in series forms a configuration that can be used as a circuit for filtering signals. If the output is taken across the capacitor the circuit behaves as a low-pass filter and if the output is taken across the resistor the circuit behaves as a high-pass filter.
What remains constant throughout its journey if a comet is revolving around the Sun in a highly elliptical orbit? Kinetic energy Potential energy Gravitational pull Angular momentum
Correct Answer: Angular momentum Explanation: The kinetic energy of the comet changes as its speed in the orbit keeps changing. The potential energy and gravitational pull changes, because the distance of the comet from the sun keeps changing. Only the angular momentum remains constant.
Who discovered a neutron's anti-particle? Bruce Cork James Chadwick William Prout Erwin Schrodinger
Correct Answer: Bruce Cork Explanation: Correct answer: Bruce Cork Antineutron is the neutron's antiparticle which Bruce Cork discovered in the year 1956.
When a particle moves in a closed loop, what is the name of the force that moves along the path and when multiplied by the distance traveled by the particle always equals zero? Circular force Inertial force Non-conservative force Conservative force
Correct Answer: Conservative force Explanation: A conservative force is defined as a force with the property that when a particle moves in any closed loop, the force acting along the path multiplied by the distance travelled always equals zero. Examples include the gravitational force, spring force, etc.
What magnetic substance has the orbits and spin axes of electrons in its atoms so oriented that their fields cancel each other out? Paramagnetic substance type Ferromagnetic substance type Diamagnetic substance type None of the above
Correct Answer: Diamagnetic substance type The orbits and spin axes of electron in an atom are so oriented that their field cancel each other are the magnetic substances of diamagnetic type
A battery of emf E and internal resistance r is connected across a pure resistive device of resistance R. What is the maximum power output ? E2/r E2/2r E2/3r E2/4r
Correct Answer: E2/4r Explanation: The current in the circuit is I=E/(R+r). Therefore the power output of the device is given by P=I2R=E2•R/(R+r)2 . For the given values of E and r, power output P will be maximum if dP/dR=0. Differentiating with respect to R, we get dP/dR=(1-2R/(R+r))•E2/(R+r)2. dP/dR=0 if R=r. Using R=r, the Pmax=E2/4r.
What is the force that holds the positive and negative charges of atoms and molecules? Gravitational force Magnetic force Electric force None of the above
Correct Answer: Electric force Explanation: Correct Answer: Electric force Electric force is defined as the force which holds the positive and negative charges that makes up atoms and molecules.
The electrostatic force between two charges placed in a vacuum is (F). If the charges are placed at the same distance apart in a medium of dielectric constant (K), what will be the force between them? F KF F/K K2F
Correct Answer: F/K Explanation: The Coulomb's Law for forces between two charges is F= (1/4πε0)q1q2/r2. Here, ε0 is being replaced by a medium with a dieletric constant K. ε0 has to be substituted by Kε0. The electrostatic force therefore, becomes F/K.
Identify the example of deposition. Melting of water into ice Formation of frost Dry ice evaporating Positive ions depositing on the negative electrode placed in a liquid
Correct Answer: Formation of frost Explanation: Deposition is a process in which gas transforms into solid (also known as desublimation). The reverse of deposition is sublimation. Deposition releases energy and is an exothermic phase change. One example of deposition is the process of formation of frost by which, in sub-freezing air, water vapor changes directly to ice without first becoming a liquid.
What should a fuse wire have? High resistivity and a high melting point Low resistivity and a high melting point High resistivity and a low melting point Low resistivity and a low melting point
Correct Answer: High resistivity and a low melting point Explanation: A fuse wire should have a high resistivity and a low melting point. When a high current flows through the fuse wire due to high resistance, heat equal to I2r is produced, which melts the fuse since it has a low melting point, and that interrupts the flow of the current.
How can a voltmeter measure voltages accurately? It must have a very low resistance. It must have a very high resistance. It must have a very high capacitance. It must have a low inductance.
Correct Answer: It must have a very high resistance. Explanation: Voltmeters are attached in parallel to the circuit components across which the voltage has to be measured. In order to prevent disturbance in the circuit due to the use of the voltmeter they have a very high resistance. This prevents the flow of current in the parallel path created due to the voltmeter and allows the circuit to remain as it was originally.
What occurs when a charged particle moves perpendicular to a uniform magnetic field? Its energy and momentum both change. Its energy changes but its momentum remains unchanged. Its momentum changes but its energy remains unchanged. Its momentum and energy remain the same.
Correct Answer: Its momentum changes but its energy remains unchanged. Explanation: Since the force exerted by the magnetic field is perpendicular to the direction of the particle motion, the speed does not change, but the velocity does. The momentum changes therefore, but the energy remains the same.
Identify the correct relationship between the displacement current JD, the electric field intensity E, and the polarization of the medium P. JD=ε0E+P. JD=E+ε0P. JD=ε0∂E/∂t+∂P/∂t. JD=ε0∂E/∂t-∂P/∂t.
Correct Answer: JD=ε0∂E/∂t+∂P/∂t. Explanation: The electric displacement field is defined as: D=ε0E+P where: ε0 is the permittivity of free space; E is the electric field intensity; and P is the polarization of the medium. Differentiating that equation with respect to time, defines the displacement current, which has two components in a dielectric, therefore: JD=ε0∂E/∂t+∂P/∂t.
A uniform wire of cross-sectional area A, and Young's modulus Y is stretched within the elastic limit. If S is the stress in the wire, what is the elastic energy density stored in the wire in terms of the given parameters? S/2Y 2Y/S S^2/2Y S^2/Y
Correct Answer: S2/2Y Explanation: Let the strain be ε. Then Y=S/ε or ε=S/Y. Now, energy density= ½ x stress x strain= ½ x S x S/Y= S^2/2Y.
Why does a balloon filled with helium stop rising after it has reached a particular altitude? The helium condenses and forms a liquid. The solar radiation changes the structure of helium. The density of air reduces. The density of air increases and the balloon bursts.
Correct Answer: The density of air reduces. Explanation: At a higher altitude, the density of air reduces. This decreases the buoyant force that is exerted on the balloon due to the air being displaced by the helium in the balloon. At the level where the weight of the balloon is equal to the buoyant force exerted on it, it stops moving higher.
What occurs in planetary motion? The speed along the orbit remains the same. The angular speed remains constant. The total angular momentum remains constant. The radius of the orbit remains constant.
Correct Answer: The total angular momentum remains constant. Explanation: The orbits of planets are elliptical. The speed of the planet and its angular speed or angular frequency keeps changing. Since no net torque acts on the planet, its angular momentum remains constant. The correct option is c.
A thin lens of optical power measuring 2.5 diopters has an object placed in front of it at a distance of 20 cm. What is the magnification of the object? Two (2) Four (4) 2.5 (Two point five) 20 (Twenty)
Correct Answer: Two (2) Explanation: M=f/(f-d0), in which f is the focal length, and d0 is the distance from the lens to the object. In the example, f=1/2.5= 0.4m. The object is placed at a distance d0=0.2m . The magnification therefore, is 0.4/(0.4-0.2)=2.
What is the kinetic energy during the oscillation when the elastic force is at its maximum? Zero At the maximum Equal to the potential energy 10 times higher
Correct Answer: Zero Explanation: Correct answer: Zero When the elastic force is maximal the body is far away from a position of stable equilibrium, potential energy has the highest value and the kinetic energy is zero, because the body speed is zero in that position.
Eight dipoles of magnitude q charges are placed inside a cube. What will be the total electrical flux through the cube? 8q/ε0 16q/ε0 q/ε0 Zero
Correct Answer: Zero Explanation: Since a dipole consists of two equal and opposite charges, the net charge of a dipole is zero. Hence, the total electrical flux through the cube is zero.
One of the postulates of the BOHR's model of a hydrogen atom states that only those stationary orbits are allowed for which orbital angular momentum is equal to an integral multiple of what value?
Correct Answer: h/2π One of the postulates of the BOHR's model of hydrogen atom states that Only those stationary orbits are allowed for which orbital angular momentum is equal to an integral multiple of h/2π Angular momentum = (m v) r m v r = n(h/2π)
For a bomb calorimeter calculation which expression is correct? q= m x S x ΔT q= S x ΔT q= S / ΔT q= m x ΔT
Correct Answer: q= S x ΔT For bomb calorimeter The amount of heat Q evolved or absorbed can be calculated by the following formula q= S x ΔT "ΔT" is the change of temperature on thermometer "S" is the specific heat of reaction mixture.
What does this reaction describe? + p → n + e+ + νe β+ Decay β- Decay Alpha decay Gamma decay
Correct Answer: β+ Decay Explanation: In β+ decay, energy is used to convert a proton into a neutron, a positron (e+) and a neutrino (νe): energy + p → n + e+ + νe . β+ decay can only happen inside nuclei when the value of the binding energy of the mother nucleus is greater than that of the daughter nucleus. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron, and a neutrino; and into the kinetic energy of these particles.
What scientist determined the radiation pressure? Maxwell Lebedev Bartoli Einstein
Correct answer: Lebedev. He determined the light pressure on the surface of solid body. The light pressure is small but responsible for the comet's tail when they pass close to sun.
What is the force that causes oscillations to come from a harmonica? Gravitational force Restitutive force Frictional force Tension forces
Correct answer: Restitutive forces These forces tend to return the body in the position of stable equilibrium. This property has the force of elasticity of metal spring.
Which process does not involve a local increase of entropy? Rusting of an iron plate Salt dissolving in water Diffusion of gas in a room Formation of ice in a refrigerator
Correct answer: formation of ice in a refrigerator Entropy increases in all processes that are spontaneous and this leads to a move to a lower, more thermodynamically stable, energy state. Among the options provided only the formation of ice in a refrigerator is not a spontaneous reaction as energy has to be supplied to achieve the same. The energy supplied is used to run the refrigerator, and the orderly ice cube has a lower entropy than the equivalent about of water. This is a process where entropy is decreasing locally.
How is the energy used when you put one foot in front of the other as you walk? Kinetic energy increases Kinetic energy decreases Both kinetic and potential energy increase Kinetic energy decreases and potential energy increases
Correct answer: Kinetic energy decreases and potential energy increases Our body acts as an inverted pendulum while placing each step. On placing the foot on the ground, the ground exerts a ground reaction force slowing down the movement thereby decreasing the kinetic energy and increasing the potential energy to maximum. This happens only when the foot touches the ground; until then the kinetic energy will be at its maximum.
Inertia of an object signifies the tendency of any matter to resist what kind of change? The center of gravity Velocity Weight Mass
Explanation: Correct Answer Velocity The definition of inertia states that it is that tendency of any matter which resists changes in its velocity.
In vertical motion a projectile has an acceleration of ay = -g. What is the acceleration of a projectile in horizontal motion? ax = 0 ax < 0 ax > 0 ax ≠ 0
Explanation: Correct Answer ax = 0 In any projectile motion horizontal acceleration satisfies the condition of ax = 0.
Identify the reason for why metals are good conductors of heat. Their surfaces are good reflectors of heat. There is a presence of a large number of free electrons. There is a violent movement of atoms. All of the above answers are correct.
Explanation: Correct Answer: There is a presence of a large number of free electrons. Presence of large number of free electrons, which conduct heat very effectively.
Calculate the amount of heat evolved in a glass calorimeter using the following information: Rise in temperature = 3.5K Specific heat of water = 4.2 Jg-1 K-1 Mass of the solution in glass calorimeter m = 200 g -2.94 kJ 2.94 kJ 29.4 kJ -29.4 kJ
Explanation: Correct Answer: -2.94 kJ q= m x S x ΔT q = 200 x 4.2 x 3.5 q = 2.94 kJ Because heat is evolve so q = -2.94 kJ
What is the heat required to raise the temperature of one gram of water through 1°C? 0.001 kcal 0.01 kcal 0.1 kcal 1 kcal
Explanation: Correct Answer: 0.001 kcal Heat required to raise the temperature of one gram of water through 1°C is 1 cal = 0.001 kcal
Conductivity of a material can be explained with its resistivity measurement. What is the resistivity range of semiconductors? 10-6<ρ<1012 Ω m 106<ρ<1018 Ω m 10-1<ρ<102 Ω m 10-4<ρ<108 Ω m
Explanation: Correct Answer: 10-4<ρ<108 Ω m Resistivity range of semiconductors is 10-4<ρ<108 Ω m.
How much power will the motor consume in 2 hours for a 3 phase AC motor with the following specifications: V=400, I =90, Power factor = 0.8? 50 KWh 100 KWh 200 KWh 9 KWh
Explanation: Correct Answer: 100 KWh P=1.73 X V X I X P.F X T P= 1.73 X 400 X 90 X 0.8 X2 P= ~ 100 KW
What would be the initial speed with which a ball would be thrown in the air at a 30 degree horizontal projection to reach a distance of 500 meters in 4 sec? 125 m/s 250 m/s 144 m/s None of the above
Explanation: Correct Answer: 144 m/s Since R=v(hor)*t, R is 500 and t is 4 sec so, Vhor =125. But this is only a component. Vi =Vhor/cos30=144.34 which is option C.
What is the work done by the engine if a Carnot's engine is working between 27°C and 127°C and taking up 800J of heat from the reservoir in one cycle? 400J 200J 100J 300J
Explanation: Correct Answer: 200J The formula for efficiency of a Carnot's engine is 1-Tc/Th. First, the temperatures have to be converted to Kelvin. Tc= 27+273=300K and Th= 127+273=400K. The efficiency= W/Q = 1- 300/400= 100/400. Q which is the heat taken from the source is 800J. Therefore, the work is 800/4=200J.
If the relative humidity is 100% and the room temperature is 25°C, what should the temperature read in a wet bulb thermometer? 15°C 25°C 30°C 45°C
Explanation: Correct Answer: 25°C No evaporation occurs when the relative humidity is 100%. Therefore, the temperature in the wet bulb thermometer is not lowered.
A coil is placed in a magnetic field whose resistance is R. The flux linked with the coil is Φ. What is the amount of charge circulated in the coil if the magnetic field suddenly reverses in direction? Φ/2R Φ/R 2Φ/R Zero
Explanation: Correct Answer: 2Φ/R The total charge circulating in a coil is equal to Total charge in flux / total resistance The reversing of magnetic field causes a change of flux by 2Φ. Hence, Q = 2Φ/R.
What is the energy acquired if a particle carrying a charge of 2 C falls through a potential difference of 3.0 V? 5 6 7 8
Explanation: Correct Answer: 6 Q= 2 c ∆V = 3 volts ∆ K.E = q x ∆V ∆ K.E = 2 x 3 ∆ K.E = 6
What is the square root of a number expressed as 4.9 x 10^17? 49 x 10^16 7 x 10^8 7 x 10^4 49 x 10^18
Explanation: Correct Answer: 7 x 10^8 Given, The number is 4.9 x 10^17 √ (4.9 x 10^17) = √ (49 x 10^16) = √ (49) x √ (10^16) = 7 x 10^8
On what does the weight of an object depend? Mass Position Mass of another object All of above
Explanation: Correct Answer: All of above Weight is the measure of gravitational force between two objects. So, all of the above mentioned factors affect weight of an object according Newton's law of gravitation.
Which type of molecular motion contributes to internal energy? Translational Rotational Vibrational All of the above
Explanation: Correct Answer: All of the above All types of molecular motion contributes to internal energy.
A point has a negative charge (q) with mass (m) is in equilibrium under an electrical field in height (h) from the ground. What is the value and direction of this electrical field? E = mg/q to the top E = q/mg to the top E = mg/q to the down E = q/mg to the down
Explanation: Correct Answer: E = mg/q to the down Two forces exist here, mg to down and F=qE will be to the top for equilibrium. So mg=qE=>E=mg/q. On the other hand because the charge of q is negative direction of E is opposite with F and so is to down.
What is the change in heat energy of a chemical reaction at a constant temperature and pressure? Enthalpy changes Bond energy Heat of sublimation Internal energy change
Explanation: Correct Answer: Enthalpy changes Whenever a change of heat energy takes place at constant temperature and pressure, then it is called enthalpy changes of reaction.
It became possible to know the speed of light (186350 mile/hour) due to the efforts of Michelson. What clue helps to measure the speed of light? Air gap Deflection Interference fringes Reflected beams
Explanation: Correct Answer: Interference fringes Interference fringes made Michelson successful to measure the speed of light which is 186350 mile/hr.
It takes approximately 150 years to remove nuclear waste safely. What is a new system that is currently being tested may be able to remove nuclear waste within 30 years? STAPO MARS NISCO HICOS
Explanation: Correct Answer: MARS To remove nuclear waste safely and quickly, the MARS system is currently being tested.
What has the same dimensions as Planck's constant? Force/distance Moment of force Moment of momentum Momentum/distance
Explanation: Correct Answer: Moment of momentum [Planck's constant] = [Moment of momentum] = [momentum × distance] = ML^2T^-1.
To discover cathode rays, investigation was performed by Sir Joseph Thomson. What was his assumption concerning cathode ray particles? They are negatively charged. They are positively charged. They have a zero charge. They have a neutral charge.
Explanation: Correct Answer: Negatively charged Sir Thomson started his investigation of cathode rays with the assumption of negatively charged particles. This assumption helped him for the prediction of path of cathode rays when these rays are passed through magnetic and electric fields. Finally this assumption was proved true.
What is the SI unit of electric flux? Nm2 C-1 Nm C-1 Nm2 C Nm2 C-2
Explanation: Correct Answer: Nm2 C-1 ?e = E.A E = F/ q N/C So Unit of the flux will be Nm2 C-1
Why do we not use X-rays in RADAR? They can damage the target. They are absorbed by the air. Their speed is low. They are not reflected by the target.
Explanation: Correct Answer: They are not reflected by the target This is because RADAR makes use of the reflected electromagnetic waves.
What occurs when light waves enter glass? They bend toward the normal of the boundary between the glass and the air. They bend away from the normal of the boundary between the glass and the air. The light waves are not effected. The glass does not change the path of the light waves.
Explanation: Correct Answer: They bend toward the normal of the boundary between the glass and the air. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media and is described quantitatively by Snell's Law.
To what is the energy of X-rays indirectly proportional? Frequency Wavelength Velocity Speed
Explanation: Correct Answer: Wavelength E = hν = hc/λ and p=h/λ.
Calculate the amount of heat evolved in a bomb calorimeter using the following information: Rise in temperature = 3.87K Specific heat =86.2 Jg-1 K-1 q = 333.59 kJ q = -333.59 kJ q = 33.359 kJ q = -33.359 kJ
Explanation: Correct Answer: q = -333.59 kJ q= S x ΔT As Rise in temperature = 3.87K Specific heat =86.2 Jg-1 K-1 By putting the values q= S x ΔT q= 86.2 x 3.87 q= 333.59 kJ As heat is evolved so q = - 333.59 kJ
What is the critical angle according to Snell's Law? 41.80 42.80 450 430
Explanation: Correct Answer: 41.80 Snell's law states Qc= Sin-1(n1/n2) Qc= Sin-1 1/1.5 Qc= 41.80
How can greater values of a charge transfer to a metal by using glass? Rub the glass with metal. Charge the glass by rubbing silk and then touch the glass with metal. Charge the glass by rubbing silk against it and then using the induction method the glass will charge the metal. It is not possible.
Explanation: Correct Answer: Charge the glass by rubbing silk against it and then using the induction method the glass will charge the metal. In the conduction a small value of charge is transferred to the metal because glass is a dielectric and all of its charges won't transfer to the metal, but in the induction method the stored charge in the metal will be bigger than the conduction.
What type of laboratory waste can be removed using a landfill, recycling, incineration, and neutralization? Metallic wastes Nuclear wastes Uranium wastes Chemical wastes
Explanation: Correct Answer: Chemical wastes Laboratory chemical wastes can be safely handled with fuel blending, Neutralization, landfill or recycling
For the ferromagnetic materials in the absence of outfield, what are the magnetic dipoles? They are parallel and with the same direction. They are parallel but not in the same direction. In the small area they are parallel and with the same direction. In the small area they are parallel and with random direction.
Explanation: Correct Answer: in the small area they are parallel and with the same direction. In the Ferromagnetic materials in the absence of outfield magnetic dipoles are in the small area parallel, with the same directions and these areas are located side by side such that the total field will be zero and along a neighborhoods areas dipoles direction construct a closed curve.
A gun with a mass of 5 kg fires a bullet with a mass of 10-2 kg at a speed of 500 m/s. What is the ratio of the distance that the gun moves backward while the bullet is in the barrel to the distance moved by the bullet? 0.5x10-3 1.0x10-3 1.5x10-3 2.0x10-3
Explanation: Correct answer: 2.0x10-3. Considering the bullet and the gun to be a single system, the linear momentum is conserved. Therefore mgvg=-mbvb or mg(Δxg/Δt)=-mb(Δxb/Δt) in which xb and xg are the distances moved by the bullet and gun. Hence, |Δxg|/|Δxb|=mb/mg=10-2/5=2 x10-3. This answer is independent of the speed of the bullet.
How do sound waves travel in helium? 2 times faster as compared to air 3 times faster as compared to air 2 times slower as compared to air 3 times slower as compared to air
Explanation: Correct answer: 3 times faster as compared to air In helium, the sound waves travel 3 times faster in comparison with air as mass of helium is lower compared to air. Hence, sound usually travels faster through materials having lower density.
What is the heat released per minute when a voltage of 10 V is applied across a resistor of 10Ω? 10 kJ 60 kJ 600 J 100KJ
Explanation: Correct answer: 600 J The power dissipated by a resistor is VI = I2R = V2/R. In this case, power = (10 Volts)2/10 Ohm = 10 Watts = 10 Joule/second. To get the heat dissipated per minute, multiply 10 Joule/second x 60 seconds/minute = 600 Joules or 0.6 KJ
Who established the relationship between the volume of gas and its temperature? Albert Einstein Amadeo Avogadro Joseph Luis Gay - Lussac Antoine Lavoisier
Explanation: Correct answer: Joseph Luis Gay - Lussac More than one century after Boyle's and Mariotte's experiments, this scientist established the relationship between gas volume and gas temperature. For certain amount of gas there is linear increase of volume with temperature on constant pressure.
Is it possible to apply the ideal gas equation on absolute zero? No, it is not possible. Under some conditions it is possible. Yes, it is possible. Rarely is it possible.
Explanation: Correct answer: No, it is not possible Ideal gas equation is applicable to gases at room temperature and atmospheric pressure. At higher pressure and lower temperatures there are significant deviations
What is a direct consequence of the diffusion and exchange of gases that are inhaled and exhaled? Pressure of these gases Partial pressure of these gases Volume of these gases Temperature of these gases
Explanation: Correct answer: Partial pressure of these gases Gases diffuse from area of higher partial pressure to area with lower partial pressure. Oxygen from lungs ( ~105 Torr) will diffuse into blood ( ~ 40 Torr) . Carbon dioxide will diffuse from blood ( ~ 45 Torr)to lungs( ~ 40 Torr) and be exhaled.
What is true of a sine wave? Semi amplitude and peak amplitude are the same. Semi amplitude is three times the root mean of the square amplitude. Peak and peak-to-peak amplitude are the same. Peak mean square and root mean square amplitude are the same.
Explanation: Correct answer: Semi amplitude and peak amplitude are same in case of a sine wave, Semi amplitude and peak amplitude are same in value, whereas, peak-to-peak amplitude is 3 times root mean square amplitude.
What is the best conductor of electricity? Gold Copper Silver Bronze
Explanation: Correct answer: Silver Silver is the best conductor medium of electricity followed by gold and copper in the 2nd and 3rd place respectively, whereas copper is the most commonly used conductor.
Which waves cannot be polarized? Transverse waves in a string Sound waves in a gas Light waves in air X-rays
Explanation: Correct answer: Sound waves in a gas. Polarization is a property of waves that describes the orientation of their oscillation. For longitudinal waves such as sound waves in fluids, the direction of oscillation is by definition, along the direction of travel, so there is no polarization. Sound waves in a gas, therefore, is the one that cannot be polarized.
Which statements is not true? A wave can be described as a disturbance that travels through a medium. In a wave there is always a force acting upon the particles that restores them to their original position. Waves involve the transport of energy and matter. In a wave the particles of the medium (water molecules) simply vibrate about a fixed position.
Explanation: Correct answer: Waves involve the transport of energy and matter. This statement is not true. Correct statement is this: "Waves involve the transport of energy without the transport of matter."
What type of energy is used to start up a motorcycle? Mechanical Chemical Nuclear Solar
Explanation: Correct answer: Chemical. Gasoline's chemical energy turns into heat and then into kinetic energy of motorcycle in motion. Part of this energy is converted into sound.
Which radioactive waste classification requires cooling as well as shielding? LLW ILW HLW Exempt waste
Explanation: Correct answer: HLW High level waste requires shielding as well as cooling due to its sufficient radioactivity, producing heat of more than 2 kW/m3.
Which series does the hydrogen absorption and emission process start and end at the hydrogen's ground state? Lyman series Balmer series Paschen series Rydberg series
Explanation: Correct answer: Lyman series The series that correlate to the atomic transitions are formed as a result of the absorption and emission process. Thus, in the Lyman series, transition starts and ends with hydrogen's ground state, whereas, in the Balmer series, the transition starts with the excited state that occurs first.
What is the logarithmic law that establishes the level scale for volume? Malus's Law Joule's law Weber-Fechner's law Thermodynamics law
Explanation: Correct answer: Weber-Fechner's law. The subjective volume can not be measured quantitatively with accuracy but it is possible to make evaluations based on the intensity using this law. Humans feel the gradation of volume as logarithm of sound intensity.
The primary coil of a transformer has 400 turns, while the secondary coil has 2000 turns. The power output from the secondary coil at 1000V is 12 kW. If the resistance of the primary is 0.2Ω, that of the secondary is 2Ω, and the efficiency of the transformer is 80%, what is the power loss in the secondary coil? 72W 144W 216W 288W
Explanation: Current in the secondary coil=12000/1000=12A. Power loss= 12^2•2=288W.
A lamp is at a height of 4 m from a table. If the height of the lamp is increased to 5 m, what would be the decrease of the illumination on the table? 25% 36% 64% 72%
Explanation: Here, E1=I/4^2, E^2=I/5^2. E2/E1=16/25, (E2-E1)/E1=(16-25)/25= -9/25= -0.36= -36%. The negative sign denotes a decrease in illuminance.
What is a streamline? It is the path a particle travels in a moving fluid. It is a pattern that appears on a moving fluid if dye is continuously injected at a single point. It is a curving line tangent to the local velocity in a flow field. Both (a) and (c)
Explanation: Streamlines are a family of curves that are instantaneously tangent to the velocity vector of the flow. These show the direction a fluid element will travel in at any point in time. Streaklines are the locus of points of all the fluid particles that have passed continuously through a particular spatial point in the past. Dye steadily injected into the fluid at a fixed point extends along a streakline Pathlines are the trajectories that individual fluid particles follow. These can be thought of as a "recording" of the path a fluid element in the flow takes over a certain period. Item A is a pathline, Item B is a streakline and item C is a streamline. Some of these lines are identical under certain steady flow conditions, but steady flow was not specified in the question.
Two waves with frequencies 100 Hz and 90 Hz are traveling toward an observer. What is the beat frequency of the sound heard by the observer? 190 Hz 10 Hz 9000 Hz 47 Hz
Explanation: The Correct answer is: 10 Hz The periodic rise or fall of intensity due to a superposition of two waves of slightly different frequencies traveling in the same direction in a medium is called beat. If f1 and f2 are the frequencies of the two waves, the beat frequency is fb=f1-f2. Here, f1=100, f2=90. The beat frequency therefore, is 10 Hz.
A spring balance reads 10 kg when a container of water is suspended from it. What will be the reading of the balance when an iron piece of mass 7.9 kg suspended by a string is immersed with half its volume inside the water in the container? The density of iron is 7.9 times greater than the density of water, or 7.9 g/cc or 7,900 kg/m3. 10 kg 10.5 kg 13.6 kg 17.2 kg.
Explanation: The Correct answer is: 10.5 kg. Density of iron=7.9x103 kgm-3. Volume of the iron piece V= mass/density=7.9/(7.9x103)=10-3 m3. The volume of the iron piece under water is V/2 = 0.5 x 10-3 m3 The submerged iron displaces 0.5 x 10-3 m3 of water, or 0.5 kg of water. That displaced water buoys up the iron, and the iron adds an equal and opposite weight to the water. Thus, the reading on the scale will increase from 10 kg to 10.5 kg.
A train covers half of the distance of its journey at a speed of 20m/s and the other half at a speed of 30m/s. What is the average speed of the train during the entire journey? 24m/s 25m/s 26m/s 27m/s
Explanation: The Correct answer is: 24 m/s Let the total journey be 2x meters. A distance x is covered with a speed of 20m/s, and the remaining distance with a speed of 30m/s. Thus, the total travel time is x/20+x/30=x/12. Average speed=total distance/total time=2x/(x/12)=24m/s.
What would be the color of the sky as seen from the Earth if there were no atmosphere? Orange Blue Red Black
Explanation: The Correct answer is: Black The color of the sky is due to the color of light that is scattered the most by the particles in the atmosphere, which is blue. If there were no atmosphere, there would be no particles to scatter the light from the sun. Hence, the sky would look black. This is why the sky looks black in pictures taken from the moon, for example.
How many base units which can be used to represent all the other physical units does the International System of Units (SI) have? 9 6 7 8
Explanation: The SI or the International system of units has 7 base units which can be used for representing all the other physical units. These are metre, kilogram, second, Ampere, Kelvin, candela and mole which represent length, mass, time, electric current, temperature, luminous intensity and amount of substance, respectively.
A compressed spring with a spring constant k is fixed at one end. It has a mass m that oscillates on a frictionless surface at the other end. What is the frequency of oscillation of the mass? 2π√(m/k) (1/2π)√(k/m) 2π√(k/m) (1/2π)√(m/k)
Explanation: The frequency of oscillation of a spring with a spring constant k and a mass m is given by (1/2π)√(k/m). When the arrangement is placed on a frictionless surface this is irrespective of the initial displacement that the spring is subject to.
An eye specialist prescribes spectacles with a combination of a convex lens of focal length 40 cm in contact with a concave lens of focal length 25 cm. What is the power of that lens combination? +1.5 D -1.5 D +6.67 D -6.67 D
Explanation: The power of the lens combination is P=P1+P2= 1/f1+1/f2 = 1/0.4+1/(-0.25) = -1.5m-1 = -1.5 D.
When finding the refractive index of a medium with reference to light, what is the reference medium to be used? Flint glass Air at standard temperature and pressure Vacuum Pure silicon
Explanation: The refractive index, n, of a medium is defined as the ratio of the velocity, c, of light in a reference medium to the velocity in the medium itself. For light, the reference medium used is vacuum, in which light travels at approximately 3x108m/s.
The human ear can only distinguish sounds which are 1/10th of a second apart. Sound travels at a speed of 343 m/s. Approximately at what distance would a reflecting object have to be for a human to be able to detect an echo? 34.3 m 68.6m 17.15m 42.4m
Explanation: The speed of sound is given as 343m/s. And for an echo to be audible the sound should take at least 1/10th of a sec to reflect back and reach the observer at the source. The time taken to travel 34.3m is .1 sec. Therefore, an echo from an object 34.3/2 = 17.15 m will be audible.
A wire of resistance 3.0Ω is stretched to twice its original length. What will be the resistance of the new wire? 1.5Ω 3.0Ω 6.0Ω 12Ω
Explanation: When the wire is stretched, its radius decreases. As the mass and density remain constant, πr12l1=πr22l2 and l2=2l1, r22= r12/2. If R1 is the original resistance of the wire, and R2 of the elongated wire, then R1=ρl1/πr12, and R2=ρl2/πr22. Thus, R1/R2=l2r12/l1r22=2x2=4, and R2=4R1=4x3=12Ω.
Monochromatic light is refracted from air into glass of refractive index μ. What is the ratio of the wavelengths of the incident and refracted waves? 1:1 1:μ μ:1 μ2:1
Explanation: va=nλa and vg=nλg. Therefore, λa/λg=va/vg. But va/vg=μ. Therefore, λa/ λg=μ. Hence, the ratio of the wavelengths of the incident and refracted waves is μ:1.
The photoelectric threshold for a certain metal surface is 330Å. What is the maximum kinetic energy of the photo electron released by a radiation of wavelength 1100Å? 1 eV 2 eV 7.5 eV no electron is emitted
For electron emission the frequency of radiation should be greater than the threshold frequency. Frequency of a wave is inversely proportional to the wavelength. Hence here as the wavelength of light is 1100Å and the threshold wavelength is 330Å, the frequency of the incident light is below the threshold frequency, therefore no electrons are emitted.
Why is it impossible to isolate magnetic poles? Magnetic field lines always make complete loops. Current through wire produces a magnetic field oriented according to the right-hand grip rule. The torque N on a small magnet is proportional both to the applied B-field, and to the magnetic momentum of the magnet. A current-carrying wire experiences a sideways force in the presence of a magnetic field.
Magnetic field lines always make complete loops. Magnetic field lines neither start nor end (although they can extend to or from infinity). Since magnetic field lines always come in loops, magnetic poles always come in N and S pairs. Cutting a magnet in half results in two separate magnets each with both a north and a south pole. Option A is the only phenomenon which explains why magnetic poles cannot be isolated.
What is the proportional relationship of the resistance (R) of a wire and the radius (r) of its cross-section? R is proportional to r. R is proportional to r2. R is inversely proportional to r. R is inversely proportional to r2.
R is inversely proportional to r2. Explanation: The resistance of a wire is given by R=ρl/πr2. Hence, the resistance increases with resistivity and length, and is inversely proportional to the area of cross-section. Thus, it is inversely proportional to the square of the radius of its cross-section.
According to the General Conference on Weights and Measures (CGPM), what is one (1) kilogram? The mass that takes 1 N of force to accelerate to 1m/s2 The mass of one (1) mole of iron atoms The mass of a cubic decimeter of water An amount of platinum-iridium that is taken to have a mass of one (1) kilogram
The Correct answer is: An amount of platinum-iridium that is taken to have a mass of one (1) kilogram. In 1889, the first CGPM sanctioned the international prototype of the kilogram, made of platinum-iridium, and declared: "This prototype shall henceforth be considered to be the unit of mass". Its record is kept at the International Bureau of Weights and Measures, under conditions specified by the First CGPM in 1889, and is intended to end any ambiguity in popular usage concerning the word, weight.
A battery of emf E and internal resistance r is connected across a pure resistive device of resistance R. Identify the equation for the maximum power output of the device. R=r R=√2 r R=2r R=4r
The current in the circuit is I=E/(R+r). Therefore the power output of the device is given by P=I2R=E2•R/(R+r)2 . For the given values of E and r, power output P will be maximum if dP/dR=0. Differentiating with respect to R, we get dP/dR=(1-2R/(R+r))•E2/(R+r)2. Thus, dP/dR=0 if R=r.
The maximum height attained by a projectile and its horizontal range are equal to each other if the projectile is projected at an angle. What is the equation for angle θ? θ= tan-1(2) θ= tan-1(3) θ= tan-1(4) θ= tan-1(5)
The maximum height of a projectile is v0^2(sin^2θ)/2g. And the horizontal range is v0^2(sin2θ)/g. For both of them to be equal, v0^2(sin^2θ)/2g = v0^2(sin2θ)/g or (sin^2θ)/2=sin2θ=2sinθcosθ or tanθ=4 or θ=tan-1(4) . Hence c is the correct choice. tan-1(4) = 1.3 rad = 76o above the horizontal - this is a short steep flight
If a ball dropped from a height H = 5 m and reached a depth of h = 15 m, what will be the deceleration caused by the water? 1.333 g 1 g 0 g 0.333 g
xplanation: Correct Answer: 1.333 g d_water=(1+H/h)g
A wire of length (L) carrying a current (I) is bent into a circle. What is the magnitude of the magnetic field at the center of the circle? πμ0I/L μ0I/2L 2πμ0I/L μ0I/2πL
πμ0I/L
