CIE iGCSE Co-ordinated Sciences-P4.3.1 Circuit diagrams and circuit components- Study Notes- New Syllabus
CIE iGCSE Co-ordinated Sciences-P4.3.1 Circuit diagrams and circuit components – Study Notes
CIE iGCSE Co-ordinated Sciences-P4.3.1 Circuit diagrams and circuit components – Study Notes -CIE iGCSE Co-ordinated Sciences – per latest Syllabus.
Key Concepts:
Core
- Draw and interpret circuit diagrams containing cells, batteries, power supplies, switches, resistors (fixed and variable), heaters, lamps, motors, ammeters, voltmeters and fuses, and know how these components behave in the circuit
Supplement
- Draw and interpret circuit diagrams containing generators and light-emitting diodes (LEDs), and know how these components behave in the circuit
CIE iGCSE Co-Ordinated Sciences-Concise Summary Notes- All Topics
Circuit Diagrams and Components
Power Sources
- Cell: Single source of electrical energy. Provides a small voltage (e.g. 1.5 V). Symbol = one long line (positive) and one short line (negative).
- Battery: Two or more cells connected in series. Provides a higher voltage. Symbol = multiple pairs of long and short lines.
- Power supply: Alternative to batteries, provides a controlled d.c. or a.c. source.
Switch
- Used to open (off) or close (on) the circuit.
- Symbol = a break in the line with a pivoted arm that can connect.
- When open → no current flows. When closed → circuit complete, current flows.
Resistors
- Fixed resistor: Opposes current with a fixed resistance value. Symbol = rectangular box.
- Variable resistor (rheostat): Resistance can be adjusted. Symbol = rectangle with a diagonal arrow. Used to control current in circuits (e.g. dimming lights).
Heater
- Converts electrical energy into heat energy (high resistance wire).
- Symbol = rectangular box with short lines inside (to represent heating element).
Lamps (Bulbs)
- Convert electrical energy into light + heat.
- Symbol = a circle with a cross (×) inside.
- If current too high → filament may blow.
Motor
- Converts electrical energy into kinetic (rotational) energy.
- Symbol = circle with “M” inside.
Measuring Instruments
- Ammeter: Measures current. Symbol = circle with “A”. Always connected in series (low resistance).
- Voltmeter: Measures potential difference. Symbol = circle with “V”. Always connected in parallel across component (high resistance).
Fuse
- Safety device that melts if current is too high, breaking the circuit.
- Symbol = rectangle with a line through it (or sometimes a simple small box).
- Protects appliances from overheating and fire hazards.
Behaviour of Components in a Circuit
- Cell/Battery: Supplies electrical energy → higher voltage = stronger push of current.
- Switch: Controls whether current flows.
- Fixed Resistor: Reduces current, drops voltage.
- Variable Resistor: Adjusts current/voltage levels.
- Heater: Gets hot, transfers energy as heat.
- Lamp: Lights up when current flows. Brightness depends on current.
- Motor: Rotates faster if more current supplied.
- Ammeter: Shows current, connected in series.
- Voltmeter: Shows p.d., connected in parallel.
- Fuse: Breaks circuit if current too high.
Example: A battery, switch, lamp, and ammeter in series, with a voltmeter connected across the lamp.
- Battery pushes current around.
- Switch controls on/off.
- Ammeter measures the current through the lamp.
- Voltmeter measures voltage across the lamp.
- Lamp glows when switch closed.
Example :
In the circuit, the ammeter shows 0.6 A when the lamp is connected to a 6 V battery. What is the resistance of the lamp?
▶️ Answer/Explanation
Step 1: Formula: \(R = \dfrac{V}{I}\).
Step 2: Substitute: \(R = \dfrac{6}{0.6} = 10 \, \Omega\).
Final Answer: The lamp has a resistance of 10 Ω.
Circuit Diagrams with Generators and LEDs
Generator
A generator converts mechanical energy (from rotation) into electrical energy.
Symbol: A circle with “G” inside (for a.c. generator, often marked with a sine wave).
- Provides an alternating current (a.c.) output in most cases (used in power stations).
- Can also be represented as a source with terminals, like a battery symbol with an a.c. label.
Behaviour in Circuit:
- Drives current around a circuit when its coil rotates in a magnetic field.
- The faster it spins, the greater the voltage and current it produces.
- Produces an output voltage that varies with time (a.c.), unlike a steady d.c. from a battery.
Light-Emitting Diode (LED)
An LED is a special type of diode that emits light when current flows through it in the forward direction.
Symbol: A diode triangle with two arrows pointing outward (to show emission of light).
- Only allows current to flow in one direction (forward bias). In reverse bias, it blocks current.
Behaviour in Circuit:
- LED lights up only when connected with the correct polarity (positive to positive terminal, negative to negative).
- They require a resistor in series to limit current — otherwise they may burn out.
- Commonly used in indicators, displays, and low-energy lighting.
Interpreting Circuits
- Generator + Lamp Circuit: Generator symbol replaces the battery, providing a.c. supply to light a lamp.
- Generator + LED Circuit: LED lights up when generator’s output drives current in the forward direction. In alternating current circuits, the LED will flash on and off (only during the half-cycle when it is forward biased).
Example :
An LED is connected to an a.c. generator. Explain why the LED flashes instead of giving a steady light.
▶️ Answer/Explanation
Step 1: The generator produces alternating current → current direction reverses each half cycle.
Step 2: An LED only conducts in one direction (forward bias).
Step 3: Therefore, the LED only lights during one half of the cycle and remains off during the other half.
Final Answer: The LED flashes on and off at the frequency of the a.c. supply.