Effects of Electric Current

Science Part 1 • Class 10th

In this chapter

• Energy transfer in an electric circuit
• Heating effects of electric current
• Magnetic effects of electric current
• Electric motor
• Electromagnetic induction
• Alternating current and direct current
• Electric generator

Energy Transfer in an Electric Circuit

• A cell is the source of energy in an electric circuit.
• If a charge Q flows from A to B through a potential difference V_AB, work is done on the charge.
• The energy given by the cell is transferred to the resistance.
• The resistor converts this energy into heat energy and its temperature increases.

Heating Effect of Electric Current

Other useful forms:

Uses of Heating Effect

• Water boiler
• Electric cooker
• Electric heater
• Electric iron
• Electric bulb
• Toaster

Electrical Energy, Fuse & MCB

Short circuit

• If live and neutral wires come in contact, a large current flows.
• Large heat is produced and inflammable material may catch fire.

Fuse and MCB

• A fuse wire melts when high current flows and breaks the circuit.
• An MCB opens the switch when current suddenly increases.

Magnetic Effect of Electric Current

Fig. 4.5 — Magnetic effects of a current

This figure illustrates the concept explained in this topic. Observe the labelled parts and relate them to the working described above.

• When current flows through the wire, the magnetic needle turns.
• Reversing the current changes the direction of the needle.
• This shows that electricity and magnetism are closely related.

Magnetic Field Around a Conductor

Fig. 4.6 — Magnetic field produced around the conductor

This figure illustrates the concept explained in this topic. Observe the labelled parts and relate them to the working described above.

• Iron filings arrange themselves along the magnetic lines of force.
• The magnetic field reduces as distance from the wire increases, if current is unchanged.
• If current through the wire is increased, the intensity of magnetic field increases.

Right Hand Thumb Rule

Fig. 4.7 — Right hand thumb rule

The right thumb shows current direction and the curled fingers show the direction of magnetic field lines.

Magnetic Field of a Loop and Solenoid

Fig. 4.8 — Magnetic field produced by a current through a loop

This figure illustrates the concept explained in this topic. Observe the labelled parts and relate them to the working described above.

If there are n turns in the loop, the magnetic field is n times that produced by a single loop.

Fig. 4.9 — Magnetic field produced by current through a solenoid

This figure illustrates the concept explained in this topic. Observe the labelled parts and relate them to the working described above.

• A solenoid is a copper wire wound in a chain of loops like a spring.
• One end acts as North pole and the other as South pole.
• The magnetic field inside the solenoid is uniform.

Force on a Current-Carrying Conductor

Fig. 4.10–4.11 — Force and Fleming's left hand rule

This figure illustrates the concept explained in this topic. Observe the labelled parts and relate them to the working described above.

• When current flows through a conductor in a magnetic field, a force is exerted on the conductor.
• The force is perpendicular to both the magnetic field and the direction of current.
• If the current direction is reversed, the force direction is also reversed.
• The force is maximum when current is perpendicular to the magnetic field.

Electric Motor

Fig. 4.13 — Electric motor: Principle and Working

This figure illustrates the concept explained in this topic. Observe the labelled parts and relate them to the working described above.

Construction

• Rectangular copper wire loop
• Magnet
• Split ring
• Carbon brushes
• Axle

Working

Forces act on opposite branches of the current-carrying coil. After every half rotation, the split ring reverses the current direction, so the loop continues rotating in the same direction.

Electromagnetic Induction

Fig. 4.15 — Current produced when a conducting wire moves in a magnetic field

Relative motion between the conductor and magnetic field produces induced current.

Michael Faraday showed in 1831 that an electric current can be produced in a conductor with the help of a moving magnet.

Fig. 4.16 — Induction when current changes or coils move

A changing magnetic effect through a coil induces current in another nearby coil.

Faraday's Law of Induction

• If current in the solenoid coil is switched on or off, current is induced in the coil.
• If current in the solenoid is increased or decreased, current is induced.
• Faster displacement gives larger galvanometer deflection.

Fig. 4.17 — Fleming's right hand rule

This figure illustrates the concept explained in this topic. Observe the labelled parts and relate them to the working described above.

Galvanometer

• A small current through its coil produces a proportional rotation.
• Voltmeter and ammeter also work on the same principle.

Alternating Current and Direct Current

Fig. 4.18–4.19 — AC and DC current

DC flows in one direction, while AC changes its magnitude and direction periodically.

AC and DC — Difference

Electric Generator

Fig. 4.20 — Electric generator

Mechanical rotation of the coil changes the magnetic flux through it and produces electrical energy by electromagnetic induction.

AC Generator

• A coil is rotated between the poles of a magnet.
• Induced current is produced in the coil.
• After every half rotation the direction of induced current reverses.
• Alternating current is produced in the external circuit.

How is DC obtained?

• In a DC generator, a split ring is fixed on the axle.
• The arrangement keeps the upward-going branch connected to one brush and the downward-going branch to the other brush.
• Hence the current flows in one direction in the external circuit.

Chapter 4 — Must Remember

• Heating effect: Heat is produced in a resistor due to current.
• Joule's law: H = I²Rt.
• Right hand thumb rule: Thumb → current; fingers → magnetic field.
• Fleming left hand: Index → field; middle → current; thumb → force.
• Electric motor: Electrical energy → mechanical energy.
• Electromagnetic induction: Change in magnetic lines through a coil induces current.
• Fleming right hand: Thumb → motion; index → field; middle → induced current.
• AC: Periodically changes magnitude and direction; India = 50 Hz.
• Generator: Mechanical energy → electrical energy.

Important Questions

1. Explain Joule's law of heating.
2. Explain short circuit and overloading.
3. State the right hand thumb rule.
4. Explain the magnetic field produced by a solenoid.
5. State Fleming's left hand rule.
6. Explain construction and working of an electric motor.
7. Define electromagnetic induction and state Faraday's law.
8. State Fleming's right hand rule.
9. Differentiate between AC and DC.
10. Explain construction and working of an AC generator.
11. Explain how DC is obtained from a generator.
12. Solve numerical problems using P = VI, P = I²R, P = V²/R and H = I²Rt.