Electricity and Circuits

OCR Applied Science P1 • Interactive Teaching Resource • Board Friendly Edition

1. Charge and Current

Current is rate of flow of charge

  • In metals, current is caused by moving electrons.
  • In electrolytes, current is caused by moving ions.
  • Conventional current is shown from positive to negative.
  • Electron flow is from negative to positive.

Charge transferred: 10 C

Elementary charge: proton = +e, electron = −e, where e = 1.60 × 10⁻¹⁹ C.

2. Potential Difference, Resistance and Ohm’s Law

Simple Circuit Simulator

Potential difference is the work done per coulomb of charge moved between two points.

Current: 2.00 A

Ohm’s law: current is proportional to potential difference if temperature and other physical conditions are constant.

3. I–V Characteristics

Fixed resistor

Straight line through the origin. Resistance is constant if temperature stays constant.

Current from graph: 0.40 A

Sensors

LDR: resistance decreases as light intensity increases.

NTC thermistor: resistance decreases as temperature increases.

4. Power and Energy in Circuits

Lamp Power Simulator

Power: 24 W

Energy transferred: 240 J

Electronvolt: the energy transferred when one electron moves through a potential difference of 1 V.

5. Series and Parallel Circuits

Series circuit

Current is the same everywhere. Potential difference is shared between components.

Total resistance: 12.0 Ω

Total current: 1.00 A

Kirchhoff’s first law: current entering a junction equals current leaving.
Kirchhoff’s second law: energy is conserved around a closed loop.

6. Potential Dividers

Potential Divider Simulator

A potential divider uses two resistances to split a supply voltage. The output voltage is taken across the lower component.

Output voltage: 6.0 V

7. Practical 5: Potential Divider Fault Finding

Diagnose the potential divider

This activity gives realistic symptoms from a faulty potential divider circuit. Students should use the readings and diagram to decide what is wrong.

  • Check whether the output voltage changes when the sensor changes.
  • Check whether the voltmeter is across the output component.
  • Check whether there is a complete circuit.
  • Check whether the fixed resistor and sensor are in series.

Click “New fault” to generate a scenario.

8. Exam Practice Quiz

Question 1

Which direction is conventional current shown?

Positive to negative
Negative to positive
Only through resistors

Question 2

What happens to LDR resistance in bright light?

It increases
It decreases
It stays constant