Questions from electricity are common in the BMAT exams. They have appeared numerous times and I am sure that you may have come across some if you have done some past papers.

Even though you may have studied electricity before, it is important to start from the basics just to jog your memory.

 Quantity Symbol S.I. Unit Current I Amperes (A) Voltage V Volts (V) Power P Watts (W) Charge Q Coulombs (C) Resistance R Ohms (Ω) Time t Seconds (s)

Here are some common electricity equations:
Current = Charge ÷ Time
I = Q ÷ t

Voltage = Current x Resistance
V = I x R

Power = Voltage x Current
P = I x R

Example:

Charge = 200 C
Time = 10 s
Resistance = 20 Ω

1. Find the current
2. Find the voltage
3. Find the power

The only way to find the current from the information given is to use the equation (I = Q ÷ t).
I = 200 ÷ 10
I = 20 A

To find the voltage, we use the formula V = I x R
V = 20 x 20
V = 400 V

To find the power, we use the formula P = I x V
P = 20 x 400
P = 8000 W

You may be asked to determine whether a certain quantity can be equal to a certain equation.

Example
Prove that P = I² x R

Firstly, we know that P = I x V
We also know that V = I x R

If we substitute (V = I x R) into the equation (P = I x V), we get the following:

P = I x (I x R)
P = I x I x R
P = I² x R