Physics- P6

An electric current is a flow of charge carriers called electrons. These electrons move randomly from one atom to another. Some collide with atoms or other electrons. This is called resistance. 

The higher the resistance the lower the current.

Ohms law-Resistance = voltage                     current

The resistance of a length of wire depends on-

It's length- the longer the wire the greater the resistance

It's cross-section- the larger the area the smaller the resistance.

The material the wire is made from

Ammeters are placed in series

Voltmeters are placed in parallel

Voltage is proportional to current

R total = R1 + R2 + R3....

Two or more resistors in a circuit -

The resistance of a thermistor changes when the temperature changes.

Thermistors-

The resistance of a thermistor decreases as the temperature increases.

A thermistor can also be used in a potential divider circuit. When the temperature falls, the output voltage rises, which can be used to switch on a heater. 

Light-dependent resistors (LDR's) - 

The resistance of a light-dependant resistor decreases as the light level increases.

It's resistance is about 100 ohms in sunlight but it can be over 10 megohms in the dark.

NOT Gate-

The output is always the opposite to the input

AND Gate-

The output is on if both of the inputs are on.

OR Gate-

The output is on if only one of the two inputs is on

NAND Gate-

Is an AND gate followed by an NOT gate.

This means that if both of the inputs are on then the out put is on. However the NOT gate switches the output to the opposite to what it should be.

NOR gate- 

It is an OR gate followed by a NOT gate.

So only one of them needs to be on and then is is switched to the opposite.

Resisting

Sharing

It's logical