AP Physics Chapter 22 Study Guide
Current and Resistance

Model of Current

Charge Carriers in Metals are Electrons

Creating Current

Conservation of Current

Law of Conservation of Current – The current is the same at all points in a current carrying wire.

Defining and Describing Current

Definition of Current

Units:

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Direction of Conventional Current is the direction the positive charge carriors would travel.

Conservation of Current at a Junction

Kirchoff's Junction Law – the sum of the currents coming into a junction equals the sum of the currents leaving a junction.

Example 1

The disk drive in a portable CD player is connected to a battery that supplies it with a current of 0.22 A. How many electrons pass through the drive in 4.5 s?

Example 2

The currents through several segments of a wire object are shown in the figure below. What are the magnitudes and directions of the currents and in segments B and C?

Batteries and EMF

Connecting Potential and Current

Factors that affect the current in a wire

Resistance (R) – Opposition of a circuit to the flow of electric current.

Example 3

A potential difference of 24 V is applied to a 150 resistor. How much current flows through the resistor?

Resistance

Where L is length of the wire, A is the cross-section area, and is the material resistivity (Table 22.1 p. 732)

Example 4

Wire 1 has a length and a circular cross section of diameter D. Wire 2 is constructed from the same material as wire 1 and has the same shape, but its length is 2L, and its diameter is 2D. Is the resistance of wire 2 (a) the same as that of wire 1, (b) twice that of wire 1, or (c) half that of wire 1?

Example 5

A current of 1.82 A flows through a copper wire 1.75 m long and 1.10 mm in diameter. Find the potential difference between the ends of the wire.

Resistors and Ohm's Law

Ohmic and Nonohmic Materials

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Ohm's Law

Energy and Power

In general, energy is required to cause an electric current to flow through a circuit. The rate at which the energy must be supplied is the power.

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Example 6

A handheld electric fan operates on a 3.00 V battery. If the power generated by the fan is 2.24 W, what is the current supplied by the battery?

Example 7

A battery that produces a potential difference V is connected to a 5 W light bulb. Later, the 5 W light bulb is replaced with a 10 W light bulb. (a) In which case does the battery supply the greatest current? (b) Which light bulb has the greatest resistance?

Example 8

A battery with an emf of 12 V is connected to a 545 resistor. How much energy is dissipated in the resistor is 65 s?

Energy Usage

Example 9

A holiday goose is cooked in the kitchen oven for 4.00 h. Assume that the stove draws a current of 20.0 A, operates at a voltage of 220.0 V, and uses electrical energy that costs \$0.048 per kWh. How much does it cost to cook your goose?