A Level Physics AS: Electrical Circuits

Electrical Circuits

This topic focuses on electrical circuit analysis, including the study of series and parallel combinations of resistors, voltage dividers, potential dividers, internal resistance, electromotive force (EMF), terminal voltage, and electrical measurements using ammeters and voltmeters.

Series and Parallel Circuits

In a series circuit, the total resistance Rtotal is the sum of individual resistances:

Worked Example

Problem: Calculate the total resistance of three resistors in series: R1 = 4Ω, R2 = 6Ω, R3 = 10Ω.

Solution:

• Rtotal = R1 + R2 + R3
• Rtotal = 4Ω + 6Ω + 10Ω = 20Ω

In a parallel circuit, the total resistance can be calculated using the formula:

1/Rtotal = 1/R1 + 1/R2 + 1/R3

Worked Example

Problem: Calculate the total resistance of three resistors in parallel: R1 = 4Ω, R2 = 6Ω, R3 = 12Ω.

Solution:

• 1/Rtotal = 1/4 + 1/6 + 1/12
• 1/Rtotal = 3/12 + 2/12 + 1/12 = 6/12
• Rtotal = 12/6 = 2Ω

Voltage and Potential Dividers

A voltage divider is used to obtain a fraction of the input voltage. The output voltage Vout across a resistor in a series circuit can be calculated as:

Vout = Vin * (R2 / (R1 + R2))

Internal Resistance and EMF

The electromotive force (EMF) of a source is the voltage when no current flows. The terminal voltage Vterminal can be expressed as:

Vterminal = EMF - I * r

where I is the current and r is the internal resistance.

Electrical Measurements

Electrical measurements are crucial for analyzing circuits. Ammeters measure current, while voltmeters measure voltage. It is important to connect ammeters in series and voltmeters in parallel with the components being measured.

Worked Example

Problem: If a circuit has a total current of 2A and a voltage drop across a resistor of 10V, what is the resistance?

Solution:

• Using Ohm's Law: V = I * R
• R = V / I = 10V / 2A = 5Ω

Understanding these concepts is essential for mastering electrical circuits in A Level Physics AS.