Devices and Simple Circuits CLASS 12

What is a Circuit?

A circuit is a path through which electric current flows.

• It must be complete (closed) for current to flow.

• If the path is broken (open circuit), no current flows.

2. Basic Components of a Circuit

1. Battery or Cell – provides electric energy to push electrons around the circuit.

2. Resistor – limits the flow of current.

3. Switch – can open or close the circuit.

4. Wires – connect all the components.

5. Load (like bulb, motor) – uses the electrical energy to do work.

3. Types of Circuits

1. Series Circuit

   • Components are connected one after the other.

   • Current is the same through all components.

   • If one component stops working, the whole circuit stops.

2. Parallel Circuit

   • Components are connected side by side.

   • Current splits among the paths.

   • If one component stops working, others continue to work.

4. Semiconductor Devices in Circuits

1. Diode

   • Allows current to flow in one direction only.

   • Used for rectification (AC to DC conversion).

2. LED (Light Emitting Diode)

   • Emits light when current passes through.

   • Works only in one direction like a diode.

3. Transistor

   • Can amplify current or act as a switch.

   • Essential in circuits for electronics like amplifiers and computers.

4. Photodiode / Solar Cell

   • Converts light into electricity.

   • Used in solar panels and light sensors.

5. Simple Circuit Examples

1. Series Bulb Circuit – all bulbs glow with the same current.

2. Parallel Bulb Circuit – bulbs glow independently; if one bulb goes out, others continue.

3. Diode Circuit – allows current to flow in one direction; used in chargers.

4. Transistor Switch – small current can control a bigger current in devices.

6. Key Points to Remember

• Current flows only in a closed circuit.

• Series: same current, voltage divides.

• Parallel: voltage same, current divides.

• Semiconductor devices (diodes, transistors, LEDs) are used to control and direct current in circuits.

• Circuits are the building blocks of all electronic devices.