Physics Test 1

Determine the length of copper wire having a resistance of 2.00 ohms at 20 with area

l=((r)(a)) / resistivity

To increase the current density in a wire of length and diameter D, you can a) decrease the potential difference between the two ends of the wire. b) increase the potential difference between the two ends of the wire. c) decrease the magnitude of the electric field in the wire. d) heat the wire to a higher temperature. e) combine both (b) and (d).

. E)

Find the equivalent capacitance between points a and b in the combination of capacitors shown in the figure below. (C1 = 1.0 µF and C2 = 5.0 µF.)

(6+1)+((5*5)/(5+5))

device's capacitance if each plate has an area If a material of dielectric constant 22.5 is inserted between the plates, what is the new value of capacitance new value of mag of charge

(8.85*10^-12)(area) ---------------------------- length they are separated (capacitance)(22.5)=ans ans*(voltage of battery)

the charge on the capacitor What voltage battery would be required to store_____ C on the capacitor?

(charge)(battery) (_____)/(charge on the capacitor)

In the air over a particular region at an altitude of 500 m above the ground, the electric field is 160 N/C directed downward. At 600 m above the ground, the electric field is 90 N/C downward. What is the average volume charge density in the layer of air between these two elevations?

(electron charge)(out-in)=ans ans ----- = volume charge density 100

How many electrons should be removed from an initially uncharged spherical conductor of radius 0.200 m to produce a potential of 7.00 kV at the surface?

1) ((7*10^-3)(.2))/(8.6*10^-9)=ans 2) Ans/charge of electron

A thin, hollow sphere has a charge q = −1.90 nC evenly distributed over its surface. The radius of the charged sphere is 1.02 m and the radii of two spherical Gaussian surfaces are a = 0.500 m and b = 1.50 m, respectively. (See the figure below.) A charge of Q = 4.80 nC is placed at the center of the charged sphere. 1) electric flux through the center 2) Find the electric field there, by dividing by the sphere's area. 3)How much charge is inside the outer dashed sphere? 4)Find the electric flux through the outer Gaussian surface.

1) (4.8*10^-9)/(8.85*10^-12) 2) EF/4pi(1/2)^2 3) q+Q 4)((q+Q)*10^-9)/(8.85*10^-12)

When is the electric field @ zero? q1=-2.7uC , q2=6.2 uC

1) sqrt(q2/q1)= ans 1 2) -------- ans-1

A conductor of radius r, length and resistivity ρ has resistance R. It is melted down and formed into a new conductor, also cylindrical, with one fourth the length of the original conductor. The resistance of the new conductor is a) R/16 b) R/4 c) R d) 4R e) 16R

4. A)

The resistivity of a wire depends on a) Its length b) Its cross-sectional area c) The material out of which it is composed d) All of the given answers

2. C)

When two or more resistors are connected in series to a battery: a) The total voltage across the combination is the algebraic sum of the voltages across the individual resistors b) The same current flows through each resistor c) The equivalent resistance of the combination is equal to the sum of the resistances of each resistor d) All of the given answers

10. D)

Kirchhoff's loop rule is an example of a) Conservation of energy b) Conservation of charge c) Conservation of momentum d) None of the given answers

13. A)

In a loop in a closed circuit, the sum of the currents entering a junction equals the sum of the currents leaving a junction because a) the potential of the nearest battery is the potential at the junction. b) there are no transformations of energy from one type to another in a circuit loop. c) capacitors tend to maintain current through them at a constant value. d) current is used up after it leaves a junction e) charge is neither created nor destroyed at a junction

14. E)

When resistors are connected in parallel, we can be certain that a) The same current flows in each one b) The potential difference across each is the same c) The power dissipated in each is the same d) Their equivalent resistance is greater than the resistance of any one of the individual resistances

17. B)

A circuit consists of N resistors, all of resistance R, connected as shown below. A potential difference V is applied to the circuit. The equivalent resistance of the circuit is a) R/4 b) R c) NR/4 d) NR e) 4NR

18. C)

A car owner forgets to turn off the headlights of his car while it is parked in his garage. If the 12.0-V battery in his car is rated at 143.0 A · h and each headlight requires 24.3 W of power, how long will it take the battery to completely discharge?

2(24.3)=48.6= I*12 I=4.05A 143/4.05=35.3

Which two circuits are exactly equivalent? a) A and B b) B and C c) C and D d) D and E e) B and E The one closest to the battery

20. B)

The circuit below contains 3 100-W light bulbs and a capacitor. The emf is 110 V. Which light bulb(s) is(are) brightest? (Assume the capacitor is fully charged.) a) A b) B c) C d) A and B e) All three are equally bright there's a break between b and c but a and b are grouped together

21. D)

The resistance of the wire is a) Proportional to its length and its cross-sectional area b) Proportional to its length and inversely proportional to its cross-sectional area c) Inversely proportional to its length and proportional to its cross-sectional area d) Inversely proportional to its length and inversely proportional to its cross-sectional area

3. B)

A kilowatt-hour is equivalent to a) 1000W b) 3600s c) 3600000J/s d) 3600000J

5. D)

When resistors are connected in series a) The same power is dissipated in each one b) The potential difference across each is the same c) The current flowing in each is the same d) More than one of the given answers is true

6. C)

Jadeen says that you can increase the resistance of a copper wire by hammering the wire to make it narrower and longer. Arnell says that you can increase its resistance by heating the wire. Which one, if either, is correct, and why? a) Arnell, because the resistivity of the wire increases when it is heated. b) Arnell, because the resistivity of the wire decreases when it is heated. c) Jadeen, because the resistivity of a wire is inversely proportional to its area and directly proportional to its length d) Jadeen, because the resistivity of a copper wire does not decrease when it is hammered. e) Both are correct because (a) and (d) are both correct

7. E)

If the resistance in a constant voltage circuit is doubled, the power dissipated by that circuit will a) Increase by a factor of two b) Increase by a factor of four c) Decrease to one-half its original value d) Decrease to one-fourth its original value

8. C)

The resistivity of most common metals a) Remain constant over wide temperature ranges b) Increases as the temperature increases c) Decreases as the temperature increases d) Varies randomly as the temperature increases

9. B)

A coulomb per second is the same as a) A watt b) An ampere c) A volt-second d) A volt per second

B)

Three identical resistors are connected in series to a 12V battery. What is the voltage across any one of the resistors? a) 36V b) 12V c) 4V d) Zero

C)

What is the unit for the quantity RC? a) Ohms b) Volt-ampere/ohm c) Second d) Meters

C)

When two or more resistors are connected in parallel to a battery a) The voltage across each resistor is the same b) The total current flowing from the battery equals the sum of the currents flowing through each resistor c) The equivalent resistance of the combination is less than the resistance of any one of the resistors d) All of the given answers

D)

State four properties of conductors in electrostatic equilibrium

Field inside is 0, Property 2: Charge Resides on the Surface, field is perpendicular to the surface, surface is equipotential

The electron-volt is a unit of a) Voltage b) Current c) Power d) Energy

d

Two small metallic spheres, each of mass m = 0.218 g, are suspended as pendulums by light strings of length L as shown in the figure below. The spheres are given the same electric charge of 6.5 nC, and they come to equilibrium when each string is at an angle of θ = 5.40° with the vertical. How long are the strings?

L= sqrt( (k)(q)^2(cos(theta)) ) --------------------- (4mg(sin(theta))^3)

A uniform electric field of magnitude 3.75 N/C is directed along the +x-axis. If a 2.15 μC charge moves from (1.00, 0) m to (2.35, 0) m in this field, determine the following. (Include the sign of the value in your answer.) (c) the electric potential difference between the particle's initial and final points

V= (qEd)/q

The equivalent capacitance of the circuit shown below is ---!-----!----! =c =2C =c ---!-----!----! a) 0.2 C b) 0.4 C c) 1 C d) 4 C e) 5 C

d

Regarding the Earth and a cloud layer 750 m above the Earth as the "plates" of a capacitor, calculate the capacitance of the Earth-cloud layer system. Assume the cloud layer has an area of 1.00 km2 and the air between the cloud and the ground is pure and dry. Assume charge builds up on the cloud and on the ground until a uniform electric field of 2.00 106 N/C throughout the space between them makes the air break down and conduct electricity as a lightning bolt. (b) What is the maximum charge the cloud can hold?

[(8.85*10^-12 ) * (1000^2)]/750=ans ans(2*10^6 * 750)

Electric dipoles always consist of two charges that are a) Equal in magnitude, opposite in sign b) Equal in magnitude; both are negative c) Equal in magnitude; both are positive d) Unequal in magnitude; opposite sign

a

the circuit in the figure below has been connected for a long time. LetR1=8.20?andR2=5.40?.

a) Req = 1/(1/(1+5.4)+1/(2+8.2)) = 3.9325 ohms i = V/R = 10/3.9325 = 2.5429 A i_left = 3.9325/(1+5.4) * 2.5429 = 1.5625 A i_right = 3.9325/(2+8.2) * 2.5429 = 0.98039 A ΔV = i_right * 2 - i_left * 1 = 0.98039 * 2 - 1.5625 * 1 = 0.398 V b) V/V0 = e^(-t/(3.9325*1e-6)) 1/4 = = e^(-t/(3.9325*1e-6)) t = 5.45 μs

For the potential v=3x^2z-2yz^3, what is the corresponding electric field at the point (2,2,2)?

a)-24i+16j+36

A positive point charge q is placed off center inside an uncharged metal sphere insulated from the ground as shown. Where is the induced charge density greatest in magnitude and what is its sign?

a)A; negative.

A point charge +Q is located on the x axis at x = a, and a second point charge −Q is located on the x axis at x = −a. A Gaussian surface with radius r = 2a is centered at the origin. The flux through this Gaussian surface is

a-zero because the negative flux over one hemisphere is equal to the positive flux over the other.

The electric field shown (arrows pointing down. a lot pointing towards the right)

aIncreases to the right

A large negatively charged object is placed on an insulated table. A neutral small metallic ball rolls straight toward the object, but stops before it touches it. A second neutral small metallic ball rolls along the path followed by the first ball, strikes the first ball, and stops. The first ball rolls forward, but doesn't touch the negative object. At no time does either ball touch the negative object. What is the final charge on each of the small metallic balls?

aa) The first ball is positive, and the second ball is negative

For an electron moving in a direction opposite to the electric field a) Its potential energy increases and its electric potential decreases b) Its potential energy decreases and its electric potential increases c) Its potential energy increases and its electric potential increases d) Its potential energy decreases and its electric potential decreases

b

One Joule per Coulomb is a a) Newton b) Volt c) Electron-Volt d) Farad

b

The equivalent capacitance of the circuit shown below is a--! !-c-! !-C2-! !-C--b a) 0.2 C b) 0.4 C c) 1 C d) 4 C e) 5 C

b

An electron and proton are separated by a distance 1m. What happens to the magnitude of the force on the proton if a second electron is placed next to the first electron?

b It doubles

Is it possible to have a zero electric field value between two positive charges along the line joining the two charges?

b Yes, regardless of the magnitude of the two charges

A glass rod is rubbed with a piece of silk. During the process the glass acquires a positive charge and the silk

b acquires a negative charge

A parallel plate capacitor is charged to voltage V and then disconnected from the battery. Leopold says that the voltage will decrease if the plates are pulled apart. Gerhardt says that the voltage will remain the same. Which one, if either, is correct, and why? a) Gerhardt, because the maximum voltage is determined by the battery. b) Gerhardt, because the charge per unit area on the plates does not change. c) Leopold, because charge is transferred from one plate to the other when the plates are separated. d) Leopold, because the force each plate exerts on the other decreases when the plates are pulled apart. e) Neither, because the voltage increases when the plates are pulled apart.

c

A surface on which all points are at the same potential is referred to as a) A constant electric force surface b) A constant electric field surface c) An equipotential surface d) An equivoltage surface

c

Several electrons are placed on a hollow conducting sphere. They a) Clump together on the sphere's outer surface b) Clump together on the sphere's inner surface c) Become uniformly distributed on the sphere's outer surface d) Become uniformly distributed on the sphere's inner surface

c

An originally neutral electroscope is briefly touched with a positively charged glass rod. The electroscope

c becomes positively charged

An uncharged spherical conducting shell surrounds a charge −q at the center of the shell. Then charge +3q is placed on the outside of the shell. When static equilibrium is reached, the charges on the inner and outer surfaces of the shell are respectively

c) +q, +2q.

An uncharged spherical conducting shell surrounds a charge −q at the center of the shell. The charges on the inner and outer surfaces of the shell are respectively

c) +q, −q.

A sphere A carries a net positive charge, and sphere B is neutral. They are placed near each other on an insulated table. Sphere B is briefly touched with a wire that is grounded. Which statement is correct?

c) Sphere B is now negatively charged

. Four electrons move from point A to point B in a uniform electric field as shown below. Rank the electrons in diagrams I through IV by the changes in potential from most positive to most negative when traveling from A to B.

c)III > I = IV > II

Is it possible to have a zero electric field value between a negative and positive charge along the line joining the two charges?

c)No, a zero electric field cannot exist between the two charges

Two concentric imaginary spherical surfaces of radius R and 2R respectively surround a positive point charge −Q located at the center of the surfaces. When compared to the electric flux Φ1 through the surface of radius R, the electric flux Φ2 through the surface of radius 2R is

c. Φ2 = Φ1.

A 15.2-g piece of Styrofoam carries a net charge of -0.752 µC and is suspended in equilibrium above the center of a large, horizontal sheet of plastic that has a uniform charge density on its surface. What is the charge per unit area on the plastic sheet?

charge per unit= 2(E0)(m)(g) ------------ q

A negative charge is moved from point A to point B along an equipotential surface a) The negative charge performs work in moving from point A to point B b) Work is required to move the negative charge from point A to point B c) Work is both required and performed in moving the negative charge from point A to point B d) No work is required to move the negative charge from point A to point B

d

A parallel plate capacitor is connected to a battery and charged to voltage V. Leah says that the charge on the plates will decrease if the distance between the plates is increased while they are still connected to the battery. Gertie says that the charge will remain the same. Which one, if either, is correct, and why? a) Gertie, because the maximum voltage is determined by the battery. b) Gertie, because the capacitance of the capacitor does not change. c) Leah, because the capacitance decreases when the plate separation is increased. d) Leah, because the capacitance increases when the plate separation is increased. e) Neither, because the charge increases when the plate separation is increased.

d

A parallel-plate capacitor has a capacitance of C. If the area of the plates is doubled and the distance between the plates is halved, what is the new capacitance? a) C/4 b) C/2 c) 2C d) 4C

d

For a proton moving in the direction of the electric field a) Its potential energy increases and its electric potential decreases b) Its potential energy decreases and its electric potential increases c) Its potential energy increases and its electric potential increases d) Its potential energy decreases and its electric potential decreases

d

When introduced into a region where an electric field is present, an electron with initial velocity will eventually move a) along an electric field line, in the positive direction of the line. b) along an electric field line, in the negative direction of the line. c) to a point of decreased potential. d) to a point of increased potential e) as described in both (b) and (d)

d

A neutral atom always has

d the same number of protons as electrons

Which one of the diagrams below is not a possible electric field configuration for a region of space which does not contain any charges?

d) shape like a diamond

Two charges are separated by a distance d and exert mutual attractive force F on each other. If the charges are separated by a distance d/3, what are the new mutual forces?

d-d) 9F

A positively charged particle is moving in the +y-direction when it enters a region with a uniform electric field pointing in the +x-direction. Which of the diagrams below shows its path while it is in the region where the electric field exists. The region with the field is the region between the plates bounding each figure. The field lines always point to the right. The x-direction is to the right; the y-direction is up.

d... arrow pointing up and then turns right

Two charged particles, Q1 and Q2, are a distance r apart with Q2 = 5Q1. Compare the forces they exert on one another when is the force Q2 exerts on Q1 and is the force Q1 exerts on Q2.

d: f2=-f1

A parallel plate capacitor of capacitance C0 has plates of area A with separation d between them. When it is connected to a battery of voltage V0, it has charge of magnitude Q0 on its plates. It is then disconnected from the battery and the space between the plates is filled with a material of dielectric constant 3. After the dielectric is added, the magnitudes of the capacitance and the potential difference between the plates are a) C0, V0 b) C0, V0 c) C0, V0 d) 3C0, V0 e) 3C0, 3V0

e

Which of the following represents the equipotential lines of a dipole?

e, ]0)!(0[

A positive point charge q is placed at the center of an uncharged metal sphere insulated from the ground. The outside of the sphere is then grounded as shown. Then the ground wire is removed. A is the inner surface and B is the outer surface. Which statement is correct?

e-The charge on A is −q; there is no charge on B.

A small, 2.00-g plastic ball is suspended by a 20.7-cm-long string in a uniform electric field as shown in the figure below. If the ball is in equilibrium when the string makes a 13.9° angle with the vertical, what is the net charge on the ball?

q= mgtan(theta) --------------- E

An electron and a proton are each placed at rest in a uniform electric field of magnitude 566 N/C. Calculate the speed of each particle 52.8 ns after being released.

q=Fnet/mass of electron or proton=ans (ans)(time*10^-9)= speed

The three charged particles in the figure below are at the vertices of an isosceles triangle (where d = 1.50 cm). Taking q = 8.70 µC, calculate the electric potential at point A, the midpoint of the base.

r1=sqrt (4d^2-(d^2/4)) The distance r2 of the charge to the left and the distance r3 of the charge to the right from pointA are r2 = r3 = d/2. The potential at point A is the sum of the contributions from each charge at its distance from point A as follows. V=kq((1/r1)-(1/r2)-(1/r3))

Copper contains approximately 8.46 ✕ 1028 electrons/m3 available to carry current. Suppose a copper wire has a diameter of 4.25 mm. (a) Calculate the cross-sectional area of the wire. (b) If the wire carries a current of 14.4 A, determine the drift speed of electrons through the wire.

radius=(4.25*10^-3)/2 Area=pi(r)^2 drift speed= ((A)/(8.46 ✕ 10^28)(1.602*10^-19)(1.42*10^-5)

electric potential at a distance the electric potential energy

v= kq ---- r PE=qv

speed when GPE is ___J.

v= sqrt 2(-(final-intial)-GPEatrest) --------------------------- m