AP Physics Chapter 22 Study Guide
Current and Resistance

 

Model of Current

current

 

 

Charge Carriers in Metals are Electrons

charge

 

Creating Current

electrons

 

current

 

Conservation of Current

current

 

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

 

Defining and Describing Current

current

 

Definition of Current

current

Units: ampere

 

Video

 

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

current

 

current

 

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.

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 current and current in segments B and C?

current

 

 

 

 

 

 

Batteries and EMF

battery

 

battery

 

battery

 

battery

 

Connecting Potential and Current

current

 

Factors that affect the current in a wire

current

 

current

 

current

 

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

resistance

ohm

 

Example 3

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

 

 

 

 

 

 

 

Resistance

resistivity

Where L is length of the wire, A is the cross-section area, and rho 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

ohm's law

 

Ohmic and Nonohmic Materials

ohmic

nonohmic

 

Video

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.

power

or

power

or

power

 

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 picture resistor. How much energy is dissipated in the resistor is 65 s?

 

 

 

 

 

 

 

 

 

Energy Usage

picture

 

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?