Describe the main difference between insulators and conductors.

• Insulators do not conduct electricity because their electrons are more tightly bound to the nucleus of the atom.

• Explain why you are able to stick a balloon to the wall after rubbing it on your head.

When you rub the balloon on your head electrons are removed from your hair and

spread out on the balloon. When you place the balloon on the wall it causes the electrons in the wall to shift away from the balloon creating a positively charged wall

which then attracts the balloon. (Induction)

• What is the force (magnitude and direction) between a 2 X 10-5 coulomb point charge and a -5 X 10-4 coulomb point charge when they are placed 25 cm apart?

1440 N

Attracted to each other

• Is the net electric force on the +q charge in case A greater than, less than or equal to the net electric force in case B? EXPLAIN

• What is the direction of the force in both cases?

• Case A is greater then case B because all force from the charge is in the X direction whereas in case B some of the force is in the Y direction and is cancelled out.

• To the left.

• Why is it best to stay inside a car during a lightening storm.

• The electrical charge is spread out on the outside of the car creating a Faraday cage.

What are the units of measurement for each of the following?

ChargeVoltageCurrentResistancepower

Charge – Coulomb (C)Voltage – Volts (V)Current – Amperage (A)Resistance – Ohms ( )Power – Watts (W)

• What happens to the resistance of a wire in each of the following cases?

a. The length of the wire increases.

b. The width of the wire increases.

c. The temperature increases.

a. Resistance increases

b. Resistance decreases

c. Resistance increases

• When connected to a 120-volt power supply, how much current exists in a light bulb that has a resistance of 200 ohms?

0.6 A

Fluorescent light bulbs use 13 Watts of energy where as incandescent light bulbs use 60 watts. If a light is on 6 hours a day, 7days a week and the electric rate is $0.10/kwh, how much money will you save in a year using 10 florescent light bulbs versus 10 incandescent light bulbs?

$102.90

• The circuit at right contains 4 identical bulbs. Rank the bulbs in order of increasing brightness.

A

C

BD

Ranking: A>D>B=C

• You want to use two light bulbs to light a room but only have one battery to power them. Will the greatest possible light be produced by hooking them up in series or in parallel? Explain.

• Parallel – Because you will decrease the resistance which will then increase the current. More flow = more glow

• The circuit at right consists of 3 identical bulbs. Initially, the switch is closed and all bulbs are the same brightness. What will happen to the brightness of bulb A if the switch is opened?

switch

A B C

• It will stay the same.

• Draw a circuit that has two 20 ohm resistors in parallel and a 60 volt energy source.

• What is the total resistance?

• What is the current flowing through each resistor?

• What is the current flowing through the battery?

10 ohms3 amps6 amps

• Find the total resistance of the circuit.

• Find the current through the battery.

3

2 3

90 V

3

9

• 13.5 ohms

• 6.7 Amps

A) Find the total resistance of the circuit.

B) Find the current through the battery.

4 ohms

5 Amps

Most household wires can only carry a maximum of 15 A of current from a 120 volt line. Can you use a 1000 Watt coffee maker, a 300 Watt mixer and a 700 watt griddle at the same time on the same circuit?

No – 16.6 amps

• Emily pushes the shutter button on her camera and the flash unit releases the 4.5 X 10-3 C of charge that was stored in a 500 micro-farad capacitor. What is the voltage across the capacitor.

9V

• The THHS array has produced 2668 KWH in the last 6 months.

If an average home uses 900 KWH per month, what % of the electricity will this array supply?

• 49%