Electric Current CBSE Notes | Class 7 Science
1. What is Electric Current?
Electric Current: The flow of electric charge through a conductor is called electric current.
➥ The SI unit of electric current is Ampere (A).
➥ Electric current (I) = Charge (Q) / Time (t)
➥ Electric current is measured by Ammeter.
2. Symbols of Electrical Components in a Circuit
| Component | Symbol |
|---|---|
| Electric Cell | + |───| - |
| Battery | + |───| - |───| + |
| Bulb | ⏚ |
| Switch (Open) | ⏇ |
| Switch (Closed) | ⏈ |
| Resistor | —VVV— |
3. Heating Effect of Electric Current
➥ When electric current flows through a conductor, heat is produced. This is called the heating effect of electric current.
Factors Affecting Heat Produced:
1. Amount of current
2. Resistance of the wire
3. Time of current flow
Applications:
1. Electric iron
2. Electric heater
3. Electric kettle
4. Magnetic Effect of Electric Current
➥ When an electric current flows through a wire, it produces a magnetic field around it.
Experiment: Place a compass near a current-carrying wire; the needle deflects due to the magnetic field.
Applications:
1. Electric motor
2. Electric bell
3. Magnetic cranes
5. Electromagnet
➥ A temporary magnet created by passing electric current through a coil of wire wound around a soft iron core.
Uses:
1. Used in electric bells
2. Used in lifting heavy objects
3. Used in medical devices like MRI machines
6. Electric Bell
Working Principle: An electric bell works on the principle of the magnetic effect of electric current.
Working:
1. When the switch is pressed, current flows through the electromagnet.
2. The electromagnet attracts the hammer, which strikes the gong to produce sound.
3. When the hammer moves, the circuit breaks, stopping the current, and the process repeats.
7. Precautions to Be Taken While Working with Electricity
1. Never touch electrical appliances with wet hands.
2. Use proper insulation for wires.
3. Do not overload sockets.
4. Turn off the main switch during electrical repairs.
5. Keep flammable materials away from electrical appliances.
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