physics 1010 amiri, exam 3

The voltage difference is 4.8 V and 7.2 V respectively.

40-ohm and 60-ohm resistors are connected in series to a 12-V battery. The current flowing through each resistor is 0.12A through both resistors, what is the voltage difference across each resistor?

0.12 A flows through both resistors.

40-ohm and 60-ohm resistors are connected in series to a 12-V battery. What is the current flowing through each resistor?

Either way.

A balloon will stick to a wooden wall if the balloon is charged:

The kinetic energy of falling water adds thermal energy to the pool of water below.

Based on his experiments, Joule proposed that the water in a pool at the bottom of waterfall should have a higher temperature than at the top. Why this might be so?

The force decreases to 1/4 of its original value.

What happens to the electric force between two electric charges if the distance between them is doubled?

Calorie is a unit for heat. Heat is a form of energy and can be specified in "joules". However, due to historical reasons, calorie is normally used in conjunction with heat. One calorie is the amount of heat (energy) to change the temperature of one gram of water by 1 degree Celsius.

What is "calorie" and what is its definition?

Electric currents are carried by electrons. These electrons normally interact with the atoms (actually ions) in the material which results in a resistance against their motion.

What is electric resistance?

Specific heat is the amount of heat to change the temperature of 1 gram of any substance by 1 degree Celsius. Based on the previous question, specific heat of water is 1cal/gram(degree C).Most common substances have specific heats much smaller than the specific heat of water.

What is specific heat?

Generator.

A device that transforms mechanical energy into electrical energy is a:

North pole.

Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a

0.25 A.

A 24-ohm resistor in a circuit has a voltage of 6 volts. What is the current through this resistor?

13.5 W.

A 9-V batter in a circuit, produces a current of 1.5 A. How much power is being delivered by the battery?

6 A.

A charge of 30 C passes at a steady rate through a resistor in a time of 5 s. What is the current through the resistor?

25A

A clothes dryer uses 5500 W of power when connected to a 220-V ac line. How much current does the dryer draw from the line?

Both the same.

A container of hydrogen gas has the same temperature as a container of oxygen gas. The gas atoms having the greater average kinetic energy are the:

Hydrogen.

A container of hydrogen gas has the same temperature as a container of oxygen gas. the gas atoms having the greater average velocity are the

Motor.

A device that transforms electrical energy to mechanical energy is a:

The temperature of metal will increase by transfer of mechanical energy to thermal energy.

A hammer is used to pound a piece of soft metal into a new shape. If the metal is thermally insulated from its surroundings, will its temperature change due to the pounding?

The needle will be deflected away from north toward a north- east direction.

A horizontal wire is oriented along a north-south line, and a compass is placed above it. An electric current flows north through the wire. Will the needle of the compass deflect?

Repel or attract.

A main difference between gravitational and electric forces is that electrical forces:

No; a charge particle at rest is not affected by a magnetic field.

A positive charge particle is momentarily at rest in a magnetic field. Is there magnetic force acting on this particle?

15 turns.

A step-down transformer converts a voltage of 120 V to 6 V. If there are 300 turns in the primary, how many turns should there be in the secondary?

15.7 ohms.

A toaster draws a current of 7 A when it is connected to a 110-V. The power consumption of this toaster is 770W, what is the resistance of the heating element of the toaster?

770 W.

A toaster draws a current of 7 A when it is connected to a 110-V. What is the power consumption of this toaster?

2 A.

A transformer has 15 turns of wire in the primary and 60 turns in the secondary. The transformer is connected to an ac source of 110 volts. The output voltage in the secondary is 440V. If a current of 8 A flows through the primary circuit, what is the induced current in the secondary?

440 V.

A transformer has 15 turns of wire in the primary and 60 turns in the secondary. The transformer is connected to an ac source of 110 volts. What is the output voltage in the secondary?

Fall closer together.

An electroscope is charged positively as shown by foil leaves that stand apart. As a negative charge is brought close to the electroscope, the leaves:

113 oF.

An object has a temperature of 45 oC. What is its temperature in Fahrenheit?

No; the battery produces a constant magnetic field. There will be no induced voltage in the secondary.

Can a transformer be use, as shown in the figure, to step up the voltage of a battery?

Heat is the internal energy transferred to a system (like a container of water or a gas cylinder). We know that energy is measured in "joules". Therefore, heat can be given in joules. For historical reasons, usually calories instead of joules are used. However, they are related to each other: 1cal=4.18joules.

Can we use "joules" as a unit for heat?

No; a step up transformer increases the output voltage but not the output energy.

Can we use a step up transformer to increase the amount of electrical energy drawn from an alternating current source?

It will decrease the brightness of the bulb.

Consider the circuit shown below. Could we increase the brightness of the bulb by connecting a wire between points A and B?

No; the wood block is an insulator and no current will flow in the circuit.

Consider the circuit shown below. Will the bulb light in this arrangement?

Heat is a form of energy. It is the internal energy (i.e. the sum of all molecular energy within a system like a container of water) which is transferred from one object to another due to their temperature difference. When you heat a container of water on the stove, internal energy is transferred from the flame (or heating element) to the water in the container. This will increase the internal energy of water molecules. Temperature is NOT a form of energy. The average kinetic energy of all molecules in a system is a MEASURE of the temperature of that system. In other words, temperature is proportional to the average kinetic energy of all molecules.

Distinguish between temperature and heat.

Specific heat determines how much heat is stored in a substance. Thus if two objects are at the same temperature, the object with higher specific heat has more energy stored in it. When an object cools off quickly, it indicates that it has a small specific heat.

Does a substance that cools off quickly have a high or low specific heat?

During the phase change, that is when water (a liquid) turns into steam, the temperature remains unchanged in spite of the fact that heat is added to the water. This is the reason that the boiling point of water is used as a "fixed point" to calibrate the temperature scale (as discussed in the computer review lesson). By the way, the same thing happens as water loses energy and turns into ice. Its temperature remains unchanged until all of the water freezes. The "ice point" is another fixed point used in calibration of thermometers.

Heat is added to a container of water is which is in state of boiling. What happens to the water temperature?

90 oF.

Heat is added to a substance initially at temperature of 30 oC, increasing its temperature to 80 oC. What is this temperature change in Fahrenheit?

Atoms are electrically neutral. Therefore, the total number of electrons is balanced the same number of protons.

How do the number of electrons in an atom compare to the number of protons?

4200 cal.

How much heat is required to raise the temperature of 70 g of water from 20 oC to 80 oC?

838 J.

If 200 cal of heat is added to a system, how much energy has been added in joules?

The potential difference or voltage across a resistor (like a light bulb, toaster, etc.) is given by the Ohm's law: V = RI. In this equation, "V" is the voltage. Doubling current, therefore, doubles the voltage across the resistor.

If the current through a certain resistance is doubled, what happens to the potential difference (i.e. voltage) across that wire?

The force between the magnets will be quadrupled.

If the distance between the south poles of two bar magnets is reduced to half its original value, what would happens to the force between the magnets?

Doubling the distance makes the denominator 4 times larger. This leads to a force which is 4 times smaller (than before moving them apart).

If the distance between two charges is doubled without changing the value of each charge, what happens to the force between them?

Doubling the distance makes the force 4 times smaller. Doubling each charge makes the force 2 times larger. But we are doubling both charges and this makes the force 4 times larger. The net effect of 4 times larger and 4 times smaller is that the force is the same as before making these changes.

If the distance between two charges is doubled, and at the same time, each is doubled, what happens to the force between them?

The force increases to 4 times its original value.

If two charges are doubled in magnitude without changing the distance between them, what happened to the electric force that they exert on each other?

The best way to understand this concept is to make a comparison with water flow in a water hose. A hose which is wide produces less resistance against the passage of water then a hose which is narrow. Therefore, resistance varies inversely with the cross sectional area. In the question above, the thin wire has a higher resistance than the thick wire.

If you have two pieces of copper wire of the same length but one is thicker than the other, which one has a higher electric resistance?

the electroscope stays as its (i.e. leaves stay away from each other at the same angle as before)

If you touch the metal ball of a charged electroscope with an uncharged glass rod held in your hand, what happens to the electroscope (i.e. what happens to the leaves of the electroscope)?

As it was shown in the computer lesson "molecular speeds", the molecules (or atoms) have a range of speeds. However, the temperature of the water in the container is determined by the AVERAGE kinetic energy of all molecules.

In a glass of water at room temperature, do all the molecules have the same speed?

The two currents are the same.

In a simple battery-and-bulb circuit, is the electric current that enters the bulb on the side nearer to the positive terminal of the battery larger than the current that leaves the bulb on the opposite side?

Current though each of the three resistors is 0.5 A.

In the circuit shown below, what is the current through each resistor? (Number resistors from left to right as, resistor 1, resistor 2, and resistor 3.)

No; the magnetic flux is proportional to the number of magnetic field lines through the area of a loop.

Is a magnetic flux the same as a magnetic field?

No, they are both at the same temperature.

Is an object with a temperature of 273.2 K hotter than an object with temperature of 0oC?

No, the electric current refers to the electric charges in motion.

Is electric current and electric charge the same thing?

Electric power is the electric energy (used or produced) per second. The unit for electric power is watts which is basically joules per second.

Is electric energy the same as electric power?

No, the temperature of 0 K is the absolute lowest temperature.

Is it possible for temperature to be lower than 0 K on the Kelvin scale of temperature?

Yes, because the internal energy includes the K.E. and P.E. of atoms and molecules.

Is it possible for the internal energy of a system to be greater than the kinetic energy of molecules and atoms?

AC.

Ordinary house current is

In the mountains.

Provided that in each case heat input is the same, boiling takes place quicker :

Decreased air pressure on the surface of a liquid lowers its boiling point.

Provided that in each case heat input is the same, boiling takes place quicker in the mountains becuase..

The leaves will be positively charges and they repel each other.

Suppose the glass rod of the previous question is used to charge a metal-foil electroscope. What happens to the leaves of the metal-foil electroscope?

Their temperatures.

The direction in which heat is conducted between two bodies depends on

Electric force.

The fundamental force underlying all chemical reactions is:

Heat.

The internal energy that is transferred from one body to another because of a temperature difference is called:

The magnet lying on the table will be repelled away from the first magnet.

The north pole of a bar magnet is brought near the north pole of a second bar magnet lying on a table. How will the second magnet tend to move?

Moving electric charge.

The source of all magnetism is:

303 K.

The temperature on a warm summer day is 86 oF. What is this temperature in Kelvin?

-10 oC.

The temperature on a windy day is 14 oF. What is the temperature in degrees Celsius?

Arrangement (a).

Two arrangements of a battery, bulb, and wires are shown below. Which of the two arrangements will light the bulb?

16 N.

Two charge particles apply a force 4 N to each other. What will be the magnitude of the force if the distance between them is decreased to one-half the original value?

3 N.

Two charged particles exert an electrostatic force of 27 N on each other. What will be the magnitude of the force if the distance between them is increased to three times the original value?

Circuit (b) causes the light bulb to light irrespective of the switch position, but circuit (a) does not light the bulb.

Two circuit diagrams are shown below. Which one will cause the light bulb to light?

Since both containers are at the same temperature, their molecules must have the SAME average kinetic energy. But kinetic energy is KE=1/2mv^2. therefore, the molecules with the larger mass will have a smaller speed in order to end up with the same kinetic energy. In this case, oxygen molecules have larger mass than hydrogen molecules. Thus the oxygen molecules will have a smaller average speed than the hydrogen molecules.

Two cylinders, one filled with oxygen and one filled with hydrogen gas, are at the same temperature. Which gas molecules have a higher average speed?

+4C and +4C.

Two identical steel balls mounted on wooden posts initially have charges of +12C and -4C. The balls are allowed to touch each other and then are separated again. What is the final charge on each ball?

The temperature of the warmer object becomes lower and that of the cooler object becomes higher.

Two object s at different temperatures are placed in contact with each other but are insulated from the surroundings. Will the temperature of either object change?

Negative.

Two pith balls are both charged by contact with a plastic rod that has been rubbed by cat fur. What kind of charge will be on the pith balls?

17.8 N.

Two positive charges of +4.45 x 10-6 C are located at a distance of 10 cm from each other. What is the magnitude of the Coulomb force (electrostatic force) between them?

The south magnetic pole attracts the north pole of a compass.

We visualized the magnetic field of the earth by imagining that there is a bar magnet inside the earth. Why did we draw this magnet with its south pole pointing north?

Freezing point is at 0C which is the same as 30F. Boiling point of water is at 100 C which is the same as 212F.

What are the temperatures for freezing water and boiling water on the Celsius and Fahrenheit scales?

Ampere is the unit for electric current. It is defined as the amount of electric charge per second through a circuit. Thus 2 amperes means that 2 coulombs of charge pass a point in the circuit every second.

What exactly is an "ampere"?

Water starts evaporating, but its temperature remains 100 oC.

What happens if we add heat to water that is at the temperature of 100 oC?

Electric resistance is measured in "ohms" and it is shown as Greek characterΩ. kΩ = Ω and 1000,000Ω =MΩ

What is the unit for measuring electric resistance?

Electric charges are measured in "coulombs" shown as "C". Charge of one electron is very small in terms of coulombs. Electron's charge is -1.6X10^-19C. Of course each proton carries the same amount of positive charge.

What is the unit of electric charge?

Similar to the law of gravity that determines the forces among masses, the Coulomb's law gives the forces between electric charges. It is given by F=k(q1q2/d^2). In the above equation, q refers to the charge and d is the distance between them. This law, like the law of gravity is an inverse square law. (Refer to the computer review lesson for more details).

What law determines the forces among electric charges?

The electrons in an atom carry negative charges and the positive charge is carried by the protons which are inside the nucleus of the atom.

What part of atom is negatively charged and what part is positively charged?

Magnetic fields are produced by electric charges that are in motion. (See the review lesson for details).

What produces a magnetic field?

They are transparent to the visible light but block the infrared radiation.

What property does glass share with carbon dioxide gas that makes them both effective in producing the greenhouse effect?

At most half as strong as the original magnet.

When a bar magnet is broken in two, each piece is:

The nylon cloth.

When a glass rod is rubbed by a nylon cloth, which of these two objects gains electrons?

The negatively charged plastic rod pushes the electrons of the ball to the opposite side. Touching the ball on the side with a finger causes these charges to be carried to the ground. Removing the finger and then the plastic rod leaves the ball with a deficiency of electrons and becomes positively charged.

When a metal ball is charged by induction using a negatively charged plastic rod, what is the sign of the charge acquired by the ball?

Positive charge.

When a metal ball is charged by induction using a negatively charged plastic rod, what kind of charge does the ball acquire?

The electrons of fur atoms are attracted toward the rubber rod. In fact some of them are transferred to the rod. As a result, the rubber rod ends up with excess electrons and become negatively charged. The fur, on the other hand, has lost some of its electrons and ends up being positively charged.

When a rubber rod is rubbed with fur, how does the rod become negatively charged?

Cooled.

When ice melts, the surrounding air is

Warmed.

When water freezes, the surrounding air is:

Negative.

When you comb your hair with a plastic comb, what kind of charge does the comb acquire?

The reason that the surface "feels" cold is that it is at a lower temperature than your body. When you touch the surface, thermal energy is transferred from your hand (high temperature system) to the cold surface (low temperature system). This is basically the definition of "heat", which is the transfer of internal energy due to temperature difference. The direction of heat transfer is always from the higher temperature to the lower temperature.

When you touch a cold surface, does cold travel from the surface to your hand or does energy travel from your hand to the cold surface?

Electric force

Which force binds atoms and molecules together?

Water has a higher specific heat and because of that, it takes longer to warm and of course, longer to cool. Sand has a low specific heat, as evidenced by how quickly the surface warms in the morning sunlight and how quickly it cools at night.

Which has a higher specific heat, water or sand?

1 cal.

Which represents the greater transfer of thermal energy, 1 J or 1 cal?

A change of 10oC.

Which spans a greater range in temperature, a change in temperature of 10oF or a change of 10oC?

The bimetallic strip is made up of two metals with different expansion (compression) rate. When heated, the metal with the high expansion rate expands more than the metal with the low expansion rate. This causes the bimetallic strip to bend.

Why does a bimetallic strip bend with changes in temperature?