One of the most useful formulas you will ever learn in the field of electrodynamics, is Ohm’s Law. Georg Simon Ohm was a very clever guy, he devised a formula that relates the voltage, current, and resistance of a circuit, hence allowing us to calculate these values at any point in the circuit.

The formula is simply:

This can be applied to any simple circuit.

Chester has an ingenious idea one day to hook up a 6 volt battery to a circuit. Once he’s done this, he plugs in his ammeter, and sees that there is a current of 3 amps flowing. What is the resistance of Chester’s home made circuit?

Answer :

This is very easy to solve, using Ohm’s Law.

V = I R

V = 6V I = 3A R = ?

6 = 3 x R

R = 6/3

R = 2 ohms

So that’s Ohm’s Law. Simple eh? Learn it well, as this formula will become very useful, particularly when we move on to more complicated circuits. In the next lesson we’ll start talking about circuits, and in particular resistance. Before we do that however, it’s time for another quick knowledge test. It’s your chance to show us how much you’ve learnt.

Questions:

1) A circuit is comprised of a variable resistor, and a battery. What happens to the current if resistance is doubled?

a) Current doubles
b) Current halves
c) Current remains the same
d) The circuit blows up

2) Which of the following statements is NOT true?

a) Voltage is inversely proportional to the value of Resistance
b) Voltage is Directly proportional to current
c) Current is inversely proportional to Resistance
d) Voltage and Resistance are always equal

3) A circuit consists of a 10ohm resistor and carrys a 5A current. What is the voltage in the circuit (in volts)?

4) Chester hooks up a current carrying wire to a voltmeter and an ammeter, which read 4V and 3A respectively. What is the resistance in the circuit (in ohms to 3 decimal places)?

5) A 6 volt power source is hooked up to a conductor with resistance 4 ohms. What current is flowing through the conductor (in amps)?

Answers:

1) B
2) A
3) 50
4) 1.333
5) 1.5