Electricity: Energy & Voltage in Circuits

Interactive learning module covering charge, current, voltage, Ohm's Law, power, energy, series and parallel circuits, and component characteristics.

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Fundamental Concepts

Learning Outcomes

  • Know that electric current is the rate of flow of charge (Q = It)
  • Understand voltage as energy transferred per unit charge

Electric Charge (Q)

Electric charge is a fundamental property of matter. It is measured in coulombs (C). One coulomb is a very large amount of charge — approximately 6.24 × 1018 electrons.

Electric Current (I)

Electric current is the rate of flow of electric charge. In metallic conductors, current is the flow of electrons. Current is measured in amperes (A), where 1 ampere = 1 coulomb per second.

Q = I × t

where Q = charge (C), I = current (A), t = time (s)

Voltage (V)

Voltage (or potential difference) is the energy transferred per unit charge. It is measured in volts (V).

1 Volt = 1 Joule per Coulomb

V = E / Q

Calculator: Q = It

Simulation: Electron Flow

Current (I = V/R): 0.12 A
Charge flow per second: 0.12 C/s
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Ohm's Law and Resistance

Learning Outcomes

  • Know and use Ohm's Law: V = IR
  • Understand how resistance affects current

Resistance (R)

Resistance is a measure of how difficult it is for current to flow through a component. It is measured in ohms (Ω).

Ohm's Law

Ohm's Law states that the current through a conductor is directly proportional to the voltage across it, provided the temperature remains constant.

V = I × R

where V = voltage (V), I = current (A), R = resistance (Ω)

Circuit Diagram for Investigating Ohm's Law

Battery Switch A Ammeter Resistor VVoltmeter
Practical: Testing Ohm's Law

Set up the circuit as shown. Adjust voltage in steps, recording current for each. Plot I vs V. The gradient equals 1/R.

I-V Characteristic Graphs

Current vs Voltage

Voltage (V)CurrentGradient = 1/R

Voltage vs Current

Current (A)VoltageGradient = R

Calculator: V = IR

Ohm's Law Graph Explorer

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Power and Energy

Learning Outcomes

  • Know and use P = IV
  • Know and use E = Pt and E = QV

Electrical Power (P)

Power is the rate of energy transfer. Measured in watts (W).

P = I × V

where P = power (W), I = current (A), V = voltage (V)

Electrical Energy (E)

E = P × t = I × V × t

where E = energy (J), P = power (W), t = time (s)

E = Q × V

where E = energy (J), Q = charge (C), V = voltage (V)

Example: A kettle has a power rating of 2000 W and is used for 3 minutes. Energy = 2000 × 180 = 360,000 J = 360 kJ

Calculator: P = IV

Calculator: E = Pt

Calculator: E = QV

Electricity Cost Calculator

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Series and Parallel Circuits

Learning Outcomes

  • Understand series and parallel circuit rules
  • Calculate total resistance, current, and voltage

Series Circuits

Components connected end-to-end, forming a single path for current.

Rtotal = R1 + R2 + R3

Current same everywhere • Voltage splits

Animated Series Circuit

Rtotal
80Ω
Current
0.15 A
V1
4.5 V
V2
7.5 V

Series Calculator

Parallel Circuits

Components connected across each other, forming multiple paths.

1/Req = 1/R1 + 1/R2

Voltage same across each branch • Current splits

⚠️ Note: Total resistance is ALWAYS LESS than the smallest individual resistance.

Animated Parallel Circuit

Req
20Ω
I1
0.20 A
I2
0.40 A
Itotal
0.60 A

Parallel Calculator

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Component Characteristics

Learning Outcomes

  • Understand I-V characteristics of resistors, filament lamps, and diodes
  • Know how LDRs and thermistors behave

I-V Characteristics Explorer

Ohmic Resistor: Current directly proportional to voltage — straight line through origin.

Light Dependent Resistor (LDR)

An LDR's resistance decreases as light intensity increases.

Resistance: 5000Ω

Thermistor (NTC)

An NTC thermistor's resistance decreases as temperature increases.

Resistance: 5000Ω

Light Emitting Diodes (LEDs)

LEDs emit light when current flows. They have a threshold voltage (~0.7V). Must be connected with correct polarity and a series resistor.

⚠️ Important: LEDs must be connected with the correct polarity (anode to positive, cathode to negative) and always use a series resistor to limit current.
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Knowledge Check Quiz

Test your understanding of electricity concepts with this interactive quiz!

1. A current of 2 A flows for 10 seconds. What is the total charge transferred?

2. A circuit has a voltage of 10 V and a current of 2 A. What is the resistance?

3. What is the power dissipated in a circuit with 5 A current and 12 V voltage?

4. In a series circuit with three bulbs, if one bulb breaks, what happens to the others?

5. When an LDR is placed in the dark, what happens to its resistance?

6. What is the unit of electrical energy?

7. In a parallel circuit, the voltage across each branch is:

8. A 2000 W kettle is used for 3 minutes. How much energy is transferred?

9. A diode allows current to flow in how many directions?

10. When an NTC thermistor is heated, its resistance: