Current electricity

Adding electrons to an uncharged atom makes it:

negatively charged, more electrons than protons

Removing electrons from an uncharged atom makes it:

positively charged, more protons than electrons

Like charges

repel each other

Different charges

attract each other

How are electrons transferred?

by friction

Uncharged objects

equal no. of positive & negative charges

Charged objects

More negative than positive charges. OR More positive than negative charges

How can an insulator become charged with static electricity?

Rub 2 insulators together, friction transfers electrons. One insulator will have a positive charge, and the other insulator will have a negative charge.

How to get a balloon to stick to a wall:

Balloon & wall has no charge. Rub balloon, it gains electrons by friction. Put the balloon near the wall, electrons are repelled from the wall. Balloon and wall attract.

What is an electric field?

Area around electric charge

Force of a field

The force of the field is strongest closer to the surface

Spark

Pd between the charged object and earth, air becomes ionised, electrons jump between charged object and the earth, energy is released as jumping heat.

Conductors

Allow electron charges to flow through them.

Insulators

Don't allow electron charged to flow through them.

Variable resistor

Fuse

Thermistor

Diode

Light emitting diode

Light dependent resistor

Current

Rate of flow of charge around a circuit. Measured in Amps.

Current (A) =

Charge (C) / time (s)

Potential difference (V) =

work done (J) / charge transferred (C)

Potential difference

Energy transferred per unit charge

Resistance (Ohms) =

Pd (V)/ current (A)

Series Circuit rules

V (pd)= other V's add up to make the V at the top.

A (current) = same throughout the circuit

Ohms (resistance) = Pd/current

Parallel Circuit rules

V (pd) = same across parallel circuits.

A (current) = same on opposite sides

Ohms (resistance) = Pd/current

Thermistor

Resistance increases as temp decreases.

Light dependent resistor

Resistance decreases as light intensity increases, less current will flow.