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CIE IGCSE Physics (0625) Circuit diagrams Study Notes

CIE IGCSE Physics (0625) Circuit diagrams Study Notes - New Syllabus

CIE IGCSE Physics (0625) Circuit diagrams Study Notes

LEARNING OBJECTIVE

  • Understanding the concepts of Circuit diagrams  

Key Concepts: 

  • Circuit Components 
  • Diodes and Light-Emitting Diodes (LEDs)

CIE iGCSE Physics (0625)  Study Notes – All topics

Circuit Components 

Circuit Components 

1. Cells, Batteries, Power Supplies

  • Cell: Provides electrical energy (DC source).
  • Battery: Two or more cells connected in series.
  • Power Supply: Can provide constant or variable DC/AC.
  • Symbol:

2. Switches

  • Function: Opens or closes a circuit to control current flow.
  • Symbol:

3. Fixed and Variable Resistors

  • Fixed Resistor: Restricts current flow by a constant amount.
  • Variable Resistor: Allows manual adjustment of resistance (used in dimmers/volume controls).
  • Symbols:

4. Heater

  • Function: Converts electrical energy to heat (e.g. kettles).
  • Symbol:  

5. Thermistor (NTC)

  • Function: Resistance decreases as temperature increases.
  • Use: Temperature sensors (e.g. fire alarms).
  • Symbol:

6. Light Dependent Resistor (LDR)

  • Function: Resistance decreases as light intensity increases.
  • Use: Automatic lights/streetlamps.
  • Symbol:         

7. Lamp (Light bulb)

  • Function: Converts electrical energy to light and heat.
  • Symbol:

8. Motor

  • Function: Converts electrical energy to mechanical motion.
  • Symbol:

9. Bell

  • Function: Converts electrical energy to sound.
  • Symbol:

10. Ammeter & Voltmeter

  • Ammeter: Measures current in amperes, placed in series.
  • Voltmeter: Measures potential difference in volts, placed in parallel.
  • Symbols:

11. Magnetising Coil

  • Function: Creates a magnetic field when current passes.
  • Use: Electromagnets in bells, relays, and motors.
  • Symbols:

12. Transformer

  • Function: Changes voltage (step-up or step-down) in AC circuits.
  • Symbol:

13. Fuse

  • Function: Safety device that melts when current exceeds safe value.
  • Symbol:

14. Relay

  • Function: Electrically operated switch controlled by another current source (e.g., low voltage circuit triggering a high voltage one).
  • Symbol:

Example:

A student builds a circuit to control the brightness of a lamp using a variable resistor. The lamp and variable resistor are connected in series to a 6 V battery.

▶️ Answer/Explanation

Step 1: The circuit is a simple series connection:

Battery → Variable Resistor → Lamp → Battery

Step 2: As the resistance of the variable resistor increases, the current in the circuit decreases.

Step 3: Lower current results in reduced brightness of the lamp.

Final Answer: The variable resistor controls the brightness of the lamp by varying the current in the circuit.

\(\boxed{\text{Increasing resistance → dimmer lamp}}\)

Example:

A 5 V circuit is used to control a 230 V lamp using a relay. The 5 V circuit includes a switch and a coil connected to the relay. When the switch is closed, the 230 V lamp lights up.

▶️ Answer/Explanation

Step 1: The low-voltage circuit includes:

Battery → Switch → Relay Coil → Battery

Step 2: When the switch is closed, current flows through the relay coil, generating a magnetic field.

Step 3: The magnetic field closes the high-voltage contacts in the separate 230 V circuit, turning the lamp on.

Final Answer: The relay allows a low-voltage control circuit to switch on a high-voltage device safely.

\(\boxed{\text{Relay = electromagnetic switch}}\)

Diodes and Light-Emitting Diodes (LEDs)

Diodes and Light-Emitting Diodes (LEDs)

1. Diodes – Behavior and Use

A diode allows current to flow in one direction only (forward direction), and blocks current in the reverse direction.

  • Use: Rectification – converting AC to DC (half-wave rectifiers).
  • Behavior:
    • Current flows only when the anode is at a higher potential than the cathode.
    • If reversed, no current flows.

2. Light-Emitting Diodes (LEDs) – Behavior and Use

An LED is a diode that emits light when current flows through it in the forward direction.

  • Use: Indicators, display panels, digital clocks, etc.
  • Behavior: Like a diode, but glows when conducting.
  • Important: LEDs must be used with a series resistor to limit current and prevent damage.

Example:

Draw a simple circuit contains a diode and a lamp connected to a battery. The diode is forward-biased.

▶️ Answer/Explanation

Step 1: In forward bias, the anode of the diode is connected to the positive terminal and the cathode to the negative terminal.

Step 2: Current flows through the circuit, allowing the lamp to light up.

Step 3: If the diode is reversed, it becomes reverse-biased, blocking the current.

Final Answer: The lamp will only light up if the diode is forward-biased.

\(\boxed{\text{Forward bias → lamp on, Reverse bias → lamp off}}\)

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