Lesson: Electric Current and Its Effects

Type 1 $–$Very Short Answer Questions (5 Q)

Question: 1

Who was the first scientist to notice the deflection of compass needle every time the current was passed through the wire?

Solution:

Hans Christian Oersted

Question: 2

What is an MCB?

Solution:

Miniature Circuit Breaker, which is used in place of a fuse.

Question: 3

Why does the coil of a heater glow?

Solution:

When electric current passes through the coil it heats up the coil so much that it turns red hot and starts glowing.

Question: 4

Why are Compact fluorescent lamps (CFLs) used?

Solution:

Compact fluorescent lamps (CFLs) used to prevent wastage of electricity by heating.

Question: 5

In fuses what kind of wires are used?

Solution:

Fuses use wires made of materials that melt and break quickly.

Type 2 $–$Short Answer Questions (5 Q)

Question: 6

What is a battery?

Solution:

When two or more cells connected together, by connecting positive terminal of a cell to the negative terminal of the next cell, this combination is called battery.

Question: 7

What is the full form of MCBs? What is its use?

Solution:

MCBs -miniature circuit breakers. These are increasingly being used in places of fuses. These are the switches which automatically turn off when current in circuit exceeds the safe limit. When we turn them on, the circuit is once again complete.

Question: 8

Why does the needle of a compass deflect when electric current passes through a wire nearby?

Solution:

The needle of a compass deflects in this case because when electric current passes through the wire nearby, it acts like a magnet making the compass needle deflect.

Question: 9

Why does a glowing bulb feel hot when touched?

Solution:

The electric current heats up the bulb filament to such an extent that it turns red hot and starts glowing, giving light, and this heat is transferred to the glass surface of the bulb making it feel hot when touched.

Question: 10

What is an electromagnet?

Solution:

An electromagnet is a metal object, which is turned into a magnet by passing electric current through a coil surrounding it. The magnetic field disappears when the current stops flowing.

Type 3 $–$ Long Answer Questions (5Q)

Question: 11

What is an open circuit?

Solution:

A circuit is said to be open when it is broken at any point and the path for movement of electric charge in not complete. The circuit in the image is an open circuit as the key is open. The current cannot flow through the circuit and the bulb cannot glow.

Question: 12

How does an electric fuse function?

Solution:

When the current flowing through a circuit is very high, the appliance in the circuit becomes far hotter than it usually is.  Due to excessive heating, the appliance gets damaged. Excessive heating also happens in case of circuit overload. To avoid such a situation, a fuse is included in the circuit. Any fuse essentially has a wire usually made of an alloy of tin and lead. This wire has low melting point. When excessive current passes through the circuit, the wire in the fuse melts and the circuit breaks before the appliance gets heated. Current stops flowing through the circuit. The appliance is, thus, saved by adding a fuse to the circuit. For different appliances, fuse of different rating is used. An appliance requiring heavy current would need fuse of higher rating. The damaged fuse is replaced by a new one for future safety.

Question: 13

Draw a simple electromagnet. Give examples of their usage in day-to-day life.

Solution:

Cranes have strong electromagnets attached to their ends for lifting heavy loads. Electromagnets are also used for separating magnetic materials from various other metallic junk. Doctors use small electromagnets to remove little pieces of magnetic material that may have entered the eye accidentally. Some toys also come with electromagnets placed inside them.

Question: 14

Draw an electric bell.

Solution:

Question: 15

Give reasons for excessive current in a wire.

Solution:

Excessive current in electrical circuits may occur when

·         The insulating cover on wires is worn off and the wires come in direct contact with each other. This may result in a short circuit.

·         There are multiple appliances connected to a single socket, which leads to circuit overload.

·         There is voltage fluctuation from the main power source.