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Physics 40s exam > Electricity > Flashcards

Flashcards in Electricity Deck (14):
1

What unit is resistance measured in?
a. Volts
b. Coloumbs
c. Amps
d. Watts
e. Ohms

e. Ohms

2

Which of the following is the same unit as Watts?
a. Volts
b. volts^2 / amps
c. Amps^2 x Ohms
d. Amps x Volts x sec

c. Amps^2 x Ohms

3

Which must always be connected in series if it is to measure a portion of a circuit correctly?
a. Ammeter
b. Voltmeter
c. Both (a) & (b)
d. neither (a) nor (b)

a. Ammeter

4

How are current and resistance related in Ohm's Law?
a. They are directly proportional
b. They are inversely proportional
c. In an inverse square relationship
d. In a direct squared relationship

b. They are inversely proportional

5

How is resistance of the conductor related to the length of the conductor?
a. They are directly proportional
b. They are inversely proportional
c. In an inverse square relationship
d. In a direct squared relationship

a. They are directly proportional

6

Given a voltage of 120 volts is applied to a load causing it to experience a current of 0.20 A, determine the resistance of the load.
a. 24 ohms
b. 6.0 x 10^2 ohms
c. 4.8 ohms
d. 7.2 x 10^4 ohms

b. 6.0 x 10^2 ohms

7

Given a diagram in which a small windmill pumps water up into the water reservoir, and given the picture is an analogy for a circuit, determine which part of the diagram would be analogous to the resistance in an electrical circuit?
a. The windmill
b. The height of the reservoir above the tank at the bottom
c. The overflow valve
d. The adjustable valve
e. The tube leading up to the reservoir

d. The adjustable valve

8

Are the two headlights of a regular automobile wired in parallel or in series?
a. Series
b. Parallel
c. Complex circuit of series and parallel components

b. Parallel

9

You connect three resistors in series across a 9-V battery. The potential difference across R1 is 2 volts, and the current through R2 is 20 mA. Determine suitable value for R1.
a. 5 ohms
b. 40 ohms
c. 0.04 ohms
d. 0.005 ohms
e. 50 ohms

e. 50 ohms

10

What is the resistance of a 60 W light bulb when it is screwed into a 120 volt lamp socket?
a. 1.0 ohm
b. 120 ohms
c. 240 ohms
d. none of the above

c. 240 ohms

11

Given electricity costs 8.2 cents/kWh, determine how much it costs to have a 15 A drier plugged into a 240 volt outlet, if it runs for 60 minutes.
a. 3.6 cents
b. 30 cents
c. $36
d. $30

b. 30 cents

12

Compare and contrast static electricity and current electricity. Include at least two similarities and two differences.

Static electricity has all its charges building in one location while current electricity has a constant flow of electrons. Static electricity is stationary while current electricity flows rapidly through a conductor and it has electrical pressure or voltage. However they both work with building up charge, just in different ways and they both involve electron flow and build up, each with the electrons moving through a conductor or "jumping" from location to location.

13

Explain what voltage is in two ways, one way - using the notion of energy and charge, and one way using a metaphor.

Voltage is really, in itself, a quantitative way of expressing the potential difference between two points in an electrical field. It's also the pressure from an electrical circuit's power source that pulses current through a conducting loop, enabling them to do the job they are being used for. Voltage can be thought of as the potential energy of water in a stream at a higher location (driving the stream) to keep flowing and moving.

14

a. A 120-V power line is protected by a 15-A fuse. (The fuse will melt and open the circuit if the current through it exceeds 15 A.) What is the maximum number of 100-W bulbs that can be simultaneously operated in parallel on this line? b. If the light bulbs were placed in SERIES would the maximum number of 100-W bulbs that could be simultaneously placed on the line increase or decrease?

a. P = V x I
P = 120 x 15 = 1800 Watts
1800 Watts / 100 W light bulbs = 18 maximum light bulbs
b. If the light bulbs were placed in series the amount that could be placed would increase because in series, IT = I1 = I2 = I3... = IN, meaning that you could place as many lightbulbs as you wanted as long as each one didn't have a current of over 15 amps.