Problem Set 7: Current, Resistance and Power

  1. Charge will move in a conductor when there is a difference in potential between the ends of the conductor. (T/F)
  1. The unit of electric current is the ampere. (T/F)
  1. Most of the electricity we buy through power companies is dc current. (T/F)
  1. When you turn on a light, electrons move at speeds near the speed of light in order to light up the light bulb. (T/F)
  1. Electrical outlets in our walls are a source of electrons to run electrical appliances. (T/F)
  1. An example of a voltage source is a dry cell/rubbing a rubber rod with fur/ a car battery.
  1. Electrical resistance in a wire depends on the wire’s conductivity/length/thickness.
  1. Is the electrical resistance in thick wires bigger/smaller/or the same size as in thin wires?
  1. When connected to a 120-V power supply, how much current exists in a light bulb that has a resistance of 240-ohms?
  1. If you accidentally grabbed the prongs of a partially plugged in 120-V electrical plug on a day when your skin resistance was 120,000 ohms, how much current would pass through your body?
  1. Why can a bird perch harmlessly on bare high voltage wires?
  1. In an alternating current circuit, electron flow is very slow/ as fast as the speed of light/ back and forth with no net motion.
  1. Current from a battery is ac or dc power?
  1. Where do the electrons come from that produce heat and light in a light bulb?
  1. How much power is used by a 6.0 V flashlight battery that draws 0.5 A of current?
  1. If a new zero-emission vehicle is powered by batteries delivering 6.00 x 102 V and its resistance is 4.4 ohms, how much charge passes through the circuit in 32.0s?
  1. What is the potential difference of a micromotor if it draws a 3.9 A current through a 0.64 ohm resistor?
  1. Recently, engineers produced a fuel cell that can generate 4.2 x 1010J of electricity in 1.1 x 103 h. What potential difference would this fuel cell place across a 40.0 ohm resistor?
  1. A generator delivered 33.6 kW to power the bus. If the generator supplied an emf of 440 V, how large was the current?
  1. A compact generator has been designed that can jump-start a car, though the generator’s mass is only about 10 kg. Find the maximum current that the generator can provide at 12.0 V if its maximum power is 850 W.

Questions #9 – 11. Use the following diagrams. The letters refer to the identical bulbs in the 4 circuits shown below.

21.  Bulb A is ______Bulb D.

a.  more bright than

b.  less bright than

c.  the same brightness as

22.  Bulb B is more bright than Bulb E.

a.  more bright than

b.  less bright than

c.  the same brightness as

23.  Bulb A is more bright than Bulb B.

a.  more bright than

b.  less bright than

c.  the same brightness as

  1. For the circuit below, solve for all of the missing data (Rtotal, Itotal, V1, I1, V2, and I2). Show your work.

R1= 16W

Vtotal= 68V

R2= 31 W

25.  For the circuit below, solve for all of the missing data (Rtotal, Itotal, V1, I1, V2, and I2). Show your work.

R1= 3.5W R2= 9.3W

Vtotal= 4.2V