3 Resistors

definition of current

The rate of flow of electric charge

Formula for Current

I = Q/t

What do wet conditons cause

They reduce the natural resistance of your hand and can cause and electric shock

What does a short circuit cause

It causes a large current to flow which can lead to a fire

What does overloading cause

It causes the main wire to ve very hot and causes a fire

Formula for PD

V = IR

Formula for resistance

R = pl/A

What affects the resistance of a resistor?

the cross sectional area, the length, the resistivity of the material, temperature

Describe the structure of a carbon resistor

It consists of a ceramic rod coated with a thin layer of carbon film. The carbon film is cut to produce a spiral conducting path of a certain resistance.

Describe the structure of a wire wound resistor

It is made by winding a thin metal wire around a cylinder made of insulating material. Cooling fins are used for resustors with high power ratings as a lot of heat is produced.

What is it meant by the power rating of a resistor?

It is the maximum power that a resistor can safely tolerate without overheating

Describe the structure of a trimpot

Two terminals of the trimpot are connected to a resistive strip. The centre terminal is connected to a wiper which can moved by turning the dial

Why is it good to connect a fixed resistor in series with a variable resistor

If the variable resistor is the only resistor along a path, a short circuit will occur is the resistance is accidentally set to zero.

Describe the effects of changung the position of the wiper on a trimpot.

This changes the resistance between the terminals A and W. It changes the length of the resistive strip through which the current flows between A and W.

Describe the parh of the current through a carbon film resistor.

The current enters the resistor from one of the end cals, flows through a spiral path formed by the carbon film and exits through the other end cap.