Current Electricity

Current Electricity

An Electric circuit needs a power source to move the electrons around the circuit. This power source has both a positive and a negative terminal.

The battery provides the energy to push the electrons through the conductors. The flow of electrons around a circuit is called current and is represented by the symbol I. Current is measured in Amperes (amps). Measuring the current that passes a point in the circuit is measured in seconds using (t) to represent time. The number of electrons – the charge (Q) that moves past a point is measured in Coulombs (C).

I = Q Current = charge moving past a point

t time

Symbols and units for current.

Symbol / Unit (quantity)
Charge / Q / C(coulombs)
Current / I / A(ampere)
Time / t / S(seconds)

The instrument used to measure the current is an ammeter represented by the symbol

This circuit diagram shows how an ammeter is connected into the circuit.

The “Push” of the battery is known as the Potential difference or Voltage. It is measured in volts using a Voltmeter.

The symbol for a voltmeter is:

This circuit diagram shows how a voltmeter is connected in the circuit, it is connected ACROSS the load (bulb) or the battery.

The amount of energy in a circuit is measured in units called Joules (J).

Voltage is measured as Joules per coulomb of charge

Symbol / Unit
Energy / E / Joules (J)
Potential Difference / V / Volts (V)
V=J/C
Charge / Q / Coulombs (C)

V =E

Q

Potential difference =Energy

Charge

Example of calculation: page 331 text

Resistance:

As the electrons travel through the circuit the meet obstacles that hinder them. These obstacles such as the light bulb are called Resistors.

This resistance can be calculated using the following information:

Resistance = Potential difference

Current

R = V

I

Symbol / Unit
Resistance / W / Ohm

Math problems: - use the GRASP method and the magic triangles.

Example:

A battery converts 72J of chemical energy. This places 12C of negative charge at the negative terminal. What is the Potential Difference between the positive and negative terminals of the battery?

G. Energy = 72J, Charge(Q) = 12C

R. Potential Difference (voltage) V

A. V =E

Q

S. V = 72

12

P. V = 6

Answer the potential difference across the negative and positive terminals of the battery is 6volts.

Math Problems. Solve the following math problems.

1.How much energy can an electric motor produce when plugged into a

110V outlet with a total charge of 50C passing through the meter?

1