• Cells have positive and negative electrodes.

• Electrons build up on the negative electrode. • Current is the amount of e- moving – coulomb

• Current is measured in Amperes.

• Voltage is the difference between the potential energy of electrons at two point in a circuit.

+ electrode

- electrode

electrolyte paste

5.5 Volt battery

5.5 Volts

0 Volts

● ●

+

-

● ●

+

-

e-

e-

Closed circuit (on) Open circuit (off)

Circuits can either be opened or closed by a switch.

Resistors, loads and

Ohm’s Law

Electrons lose energy as they move through things.

Resistor: electrical device in a circuit that takes potential energy from electrons – resistance.

Electrical symbol – R

Unit is the ohm (Ω)

The loss of potential energy over a resistor is called the “voltage drop”

Schematic Symbol

Resistors are sometimes used to reduce the energy of a circuit for safety reasons.

Any resistor that takes the energy and converts for

use – load.

Mechanical Energy Thermal Energy

● ●

+

-

e-

e-

Load• a resistor that converts energy.

Resistor• lowers energy• removed as heat

Ohm’s Law - The voltage in a wire is equal to current multiplied by resistance.

I R

V

V = I · R

I = VR

R = V I

A bulb that has 2.4 A flowing through it, has a resistance of 16 Ω. Calculate the voltage drop across the load – energy lost by the electrons to light up the bulb.

● ●

+

-

e-

e-

V = I · R

= (2.4 A) · (16 Ω)

= 38.4 V

38.4 V

A 9 V battery is hooked up to a metal wire to make a circuit. If the metal wire has a resistance of 6.5 Ω, calculate the current in the wire.

● ●

+

-

e-

e-

I = VR

9 V 6.5 Ω

=

= 1.38 A

I R

V

Voltage – Energy lost by the electrons through the circuit.

Current – Number of electrons moving through the circuit.

Resistance – the ability of a load or resistor to take energy.