NCERT Class X Science Solutions: Chapter 13 – Magnetic Effects of Electric Current Part 4

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Question 15:

State the rule to determine the direction of a

  1. Magnetic field produced around a straight conductor-carrying current,

  2. Force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and

  3. Current induced in a coil due to its rotation in a magnetic field.

Answer:

  1. Maxwell’s right hand thumb rule

  2. Fleming’s left hand rule

  3. Fleming’s right hand rule

Question 16:

Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?

Answer:

Principle:

An electric generator works on the principle of electromagnetic induction phenomenon. According to it, whenever a coil is rotated between the poles of a magnet, an induced current is set up in the coil, whose direction is given by Fleming's right-hand rule.

Result for electric generator.

Electric Generator

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Working:

When the axle attached to the two rings is rotated such that the arm AB moves up (and the arm CD moves down) in the magnetic field produced by the permanent magnet. The coil ABCD is rotated clockwise in the arrangement. By applying Fleming’s right-hand rule, the induced currents are set up in these arms along the directions AB and CD. Thus an induced current flows in the direction ABCD. If there are larger numbers of turns in the coil, the current generated in each turn adds up to give a large current through the coil. This means that the current in the external circuit flows from B2 to B1. After half a rotation, arm CD starts moving up and AB moving down. As a result, the directions of the induced currents in both the arms change, giving rise to the net induced current in the direction DCBA. The current in the external circuit now flows from B1 to B2. Thus after every half rotation the polarity of the current in the respective arms changes. Such a current, which changes direction after equal intervals of time, is called an alternating current (abbreviated as AC). This device is called an AC generator.

Question 17:

When does an electric short circuit occur?

Answer:

If either the insulation of wires used in an electrical circuit is damaged or there is a fault in the appliance, live wire and neutral wire may come in direct contact. As a result, the current in the circuit abruptly rises and short-circuiting occurs.

Question 18:

What is the function of an earth wire? Why is it necessary to earth metallic appliances?

Answer:

The metallic body of electric appliances is connected to the earth by means of earth wire so that any leakage of electric current is transferred to the ground. This prevents any electric shock to the user. That is why earthling of the electrical appliances is necessary.