 # Introduction to electricity for SQA Higher Physics 1. Short, open and closed circuits
2. Ohm's law

An open circuit is one in which there is a break such that no current can flow. A closed circuit is a complete one in which current can flow. A short circuit is one in which an incorrect connection or a damaged part will cause the current in the circuit to take a shorter route to the one intended. This may lead to a decrease in resistance in the circuit and thus an increase in current. This high current flow may damage the circuit, which is why short circuits are dangerous. Ohm's Law states that the current flowing through a component in a circuit is directly proportional to the voltage across it, given that it is at a constant temperature. This is also given as the formula: V = IR, where V is voltage, I is current and R is resistance. # 1

What is the condition required for Ohm's Law to hold?

The temperature across the component in the circuit must be constant. # 2

Given that the potential difference across a resistor is 6 V and the current flowing through it is 2 A, calculate its resistance.

Using Ohm's Law, 6 V = 2 A × R, therefore R = 6 V/2 A = 3 Ω. # 3

State Ohm's Law.

Ohm's Law states that the current flowing through a component in a circuit is directly proportional to the voltage across it, given that it is at a constant temperature. # 4

For a lamp in a circuit to light up, does the circuit have to be open or closed?

The circuit must be closed. Current will flow through the lamp in a closed circuit, and thus it will light up. # 5

Calculate the current flowing through a lamp of potential difference 16 V and resistance 4 Ω.

Using Ohm's Law, 16 V = I × 4 Ω, therefore I = 16 V/4 Ω = 4 A. End of page