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:

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

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.

or

or

**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?