Class 10 Science Chapter 12 Question Answers - Magnetic Effects of Electric Current

Q1. How will you find out the direction of the magnetic field produced by current-carrying conductor? 

Ans: The direction of the magnetic field produced by a straight wire carrying current can be determined using Maxwell’s right-hand thumb rule. This rule states:

• Hold the wire in your right hand.
• Point your thumb in the direction of the current.
• The direction your fingers curl around the wire shows the direction of the magnetic field lines.

For example, if a current-carrying wire, labelled AB, carries current vertically upwards:

• Hold the wire so your thumb points upwards towards A.
• Your fingers will curl in an anti-clockwise direction.
• This indicates that the magnetic field lines also move in an anti-clockwise direction around the wire.

Q2. What type of core should be put inside a current-carrying solenoid to make an electromagnet?

Ans: A soft iron core is placed inside a solenoid to create an electromagnet. This setup enhances the strength of the magnetic field significantly due to the following reasons:

• The soft iron core becomes magnetised by induction.
• This increases the overall magnetic field strength produced by the solenoid.

The combination of a solenoid and a soft iron core is known as an electromagnet.

Q3. Distinguish between a bar magnet and an electromagnet.
Ans: 
Q4. Explain what is short-circuiting and overloading in an electric supply. 

Ans: Short-circuiting: This occurs when the plastic insulation of the live and neutral wires is damaged, causing them to touch directly. The result is a circuit that allows a very large current to flow, generating significant heat. This excessive heat can lead to a fire hazard.

Overloading: In domestic wiring, the current depends on the power ratings of the appliances in use. If many high-power appliances are switched on simultaneously, they draw a large current from the circuit. This situation is known as overloading. The increased current can heat the copper wires to dangerous temperatures, also posing a fire risk.

Q5.  Give two reasons why different electrical appliances in a domestic circuit are connected in parallel.

Ans: Two reasons why different electrical appliances in a domestic circuit are connected in parallel:

• If one appliance is switched off or fails, other appliances continue to operate without interruption.
• All appliances receive the same voltage from the main supply, ensuring consistent performance.

Q6. Why is a fuse wire made of a tin-lead alloy and not copper? 

Ans: A fuse wire is made of a tin-lead alloy because:

• It has a low melting point, allowing it to melt easily during a fault.
• Copper, in contrast, has a high melting point, which means it would not melt quickly enough in a short circuit.

Using a tin-lead alloy ensures that the fuse operates effectively to protect the circuit.

Q7. What is a fuse wire? What is the advantage and disadvantage of using a thick fuse wire? 

Ans: A fuse is a crucial device that protects electric circuits. It consists of a wire made from a metal, such as tin or a tin alloy, which has a low melting point.

When a high current flows through the circuit, the fuse wire heats up and melts due to short-circuiting or overloading. This action breaks the circuit and stops the current, preventing damage to the appliances connected to it.

Here are the advantages and disadvantages of using a thick fuse wire:

• Advantage: A thick fuse wire can carry a higher current without melting, providing better protection for circuits with high current demands.
• Disadvantage: It may not melt quickly enough during a fault condition, which could lead to damage in the circuit or appliances.

Q8. What are magnetic field lines? How is the direction of a magnetic field at a point determined? Mention two important properties of the magnetic field lines. 

Ans: The space around a magnet where magnetic force acts is known as a magnetic field. Magnetic field lines are visual representations that indicate the direction a north pole would take if placed at any point in the field. To determine the direction of the magnetic field at a specific point:

• Imagine a hypothetical north pole at that point.
• Observe the direction in which this north pole would move due to the magnetic field.

A common example is a compass needle, which aligns itself with the magnetic field when near a magnet.

Two important properties of magnetic field lines are:

• The tangent at any point on a field line shows the direction a north pole would move if placed there.
• The density of the lines indicates the strength of the magnetic field: closer lines mean a stronger field.
• Magnetic field lines never cross, as a pole can only move in one direction at a time.

Q9. Draw a rough sketch of the pattern of field lines due to a
(i) current flowing into a circular coil and
(ii) solenoid carrying current.
Ans:
Q10. State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field. (iv) Current induced in a circuit by the changing magnetic flux due to the motion of a magnet.

Ans: (i) The direction of the magnetic field around a current-carrying conductor can be determined using Maxwell's right-hand thumb rule. This rule states:

• Hold the wire in your right hand.
• Point your thumb in the direction of the current.
• Your fingers will curl around the conductor, indicating the direction of the magnetic field lines.

(ii) The direction of the force on a current-carrying conductor in a magnetic field is found using Fleming's left-hand rule. This rule states:

• Extend your thumb, forefinger, and middle finger of your left hand so they are at right angles.
• The forefinger points in the direction of the magnetic field.
• The middle finger points in the direction of the current.
• The thumb indicates the direction of the force acting on the conductor.

(iii) The direction of the induced current in a circuit due to changing magnetic flux is determined by Fleming's right-hand rule. This rule states:

• Hold your right hand with the thumb, forefinger, and middle finger at right angles.
• The forefinger shows the direction of the changing magnetic field.
• The thumb indicates the motion of the conductor.
• The middle finger gives the direction of the induced current.

(iv) The current induced in a circuit by a moving magnet is also based on the principle of electromagnetic induction, which follows the same rules as described above.

Q11. What is the function of an earth wire? Why is it necessary to earth the metallic appliances? [Old NCERT]

Ans: The metal body of an electrical device is earthed to reduce the risk of electric shocks. This is achieved using a wire known as the earth wire, which connects the device's metal body to the ground, maintaining it at zero potential.

In a typical household circuit, there are three wires:

• Live wire
• Neutral wire
• Earth wire

One end of the earth wire is attached to the device, while the other end is connected to the ground. When we say the device is “earthed” or “grounded”, it means this connection is in place.

This setup ensures that:

• High current can safely flow to the ground from the device.
• It helps prevent electric shocks to users.