PHY 2005, Test 1, January 24, 2003

 

1. A charge of +3.0 microC is at x = 0, and a charge of -3.0 microC is at x = 6.0 m.  A third charge of -4.0 microC is placed at (x,y) = (3 m, 4 m).  What is the magnitude of the force on this third charge because of the other two charges?

 

(1) 0.73 x 10-3 N  (2) 1.5 x 10-3 N  (3) 4.1 x 10-3 N  (4) 5.2 x 10-3 N  (5) 8.1 x 10-3 N

 

2. Refer back to the previous question where a charge of +3.0 mC is at x = 0, and a charge of -3.0 mC is at x = 6.0 m.   What is the direction of the electric field at the point (x,y) = (3 m, 4 m) due to these two charges?

 

(1) in the +x direction  (2) in the –x direction  (3) in the +y direction  

(4) in the –y direction   (5) none of the choices

 

3. A positive charge q is placed a small distance d from a conducting sphere.  Which one or more of the following statements are true, depending on the sizes of the charges and the resulting amount of polarization?

a) If the sphere has a net positive charge, the charge and the sphere must repel each other.

b) If the sphere has no charge, the charge and the sphere must attract each other.

c) If the sphere has net negative charge, the charge and the sphere must attract each other.

 

(1) a   (2) b   (3) c   (4) a and b   (5) b and c

 

4. An alpha particle is composed o1f 2 protons and two neutrons (which have no charge).  The alpha particle is accelerated through a potential difference of 500 V.  How much kinetic energy is gained by the alpha particle?

 

(1) 500 eV   (2) 250 eV   (3) 1000 eV   (4) 2000 eV   (5) none of these

 

5. A dust particle having an unknown charge of q and a known mass of 2.0 x 10-8 kg is suspended against gravity between two very large charged conducting plates that are separated by 0.20 m.  The electrical potential difference between the plates is 80 volts.  What is q?

 

(1) 5 x 10-10 C  (2) 4 x 10-9 C  (3) 1 x 10-9 C  (4) 2 x 10-8 C  (5) 8 x 10-7 C

 

6. Under equilibrium conditions, which one or more of the following are true for a solid metal sphere carrying a charge -Q?

a) The charge is uniformly distributed throughout the sphere.

b) The electric field inside the sphere is zero.

c) The electric field just outside the surface of the sphere is pointed radially outward.

 

(1) a  (2) b  (3) c  (4) a and b  (5) b and c

 

7. Three capacitors CA = 2.0 mF, CB = 6.0 mF and CC = 3.0 mF are connected (in the given order) to each other in series.  A 12-V battery is connected across the system.  What is the charge on the plates of the 6.0-mF capacitor.

 

(1) 1.0 mC  (2) 2.0 mC  (3) 4.0 mC  (4) 6.0 mC  (5) none of these

 

8. The three capacitors are now placed in parallel.  The 12-V battery is connected across the system.  What is the potential difference across the 6.0-mF capacitor.

 

(1) 1 V  (2) 3 V  (3) 4 V  (4) 6 V  (5) none of these

 

9. A beam of electrons in a TV picture tube is measured to be 5.0 x 10-8 A.  How many electrons per second strike the screen from this beam?

 

(1) 8.0 x 109   (2) 1.6 x 1011  (3) 8.0 x 1011  (4) 3.1 x 1011  (5) 5.0 x 108

 

10. Refer to the circuit shown.  Find the current through the battery.

 

(1) 0.25 A   (2) 0.33 A   (3) 0.42 A   (4) 0.67 A  (5) 0.75 A

 

11. Refer to the same circuit.  Find the power expended in the 4-ohm resistor.

 

(1) 1.0 W   (2) 2.0 W   (3) 3.0 W   (4) 4.0 W   (5) none of these

 

 

 

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