Chapter 13. Magnetic Effects of Electric Current

Class 10 Science Chapter 13. Magnetic Effects of Electric Current Internal Questions and Answers :

Q1. Why does a compass needle get deflected when brought near a bar magnet?

Answer:  A compass needle gets deflected when brought near a bar magnet due to the magnetic field produced by the magnet. The compass needle aligns itself with the magnetic field lines, indicating the presence and direction of the magnetic field.

Example 13.1
A current through a horizontal power line flows in east to west direction. What is the direction of magnetic field at a point directly below it and at a point directly above it?

Answer : At a point directly below the horizontal power line, the direction of the magnetic field is vertically upward.

At a point directly above the horizontal power line, the direction of the magnetic field is vertically downward.

Internal Questions :

Q1. Draw magnetic field lines around a bar magnet.

Answer : We draw magnetic field lines around a bar magnet :

Q2. List the properties of magnetic lines of force.

Answer: The properties of magnetic lines of force or magnetic field lines are :

1. They form closed loops, starting from the north pole and ending at the south pole of a magnet.

2. They are continuous and do not have any breaks or interruptions.

3. They never intersect each other.

4. They are closer together in regions of stronger magnetic fields and farther apart in regions of weaker magnetic fields.

5. They emerge from the north pole and enter the south pole of a magnet.

6. They are used to determine the direction in which a magnetic force will act on a magnetic material or a moving charge.

Q3. Why don’t two magnetic lines of force intersect each other?

Answer: Two magnetic lines of force do not intersect each other because if they were to intersect, it would imply that a given point in space has two different directions of the magnetic field, which is not possible.

Internal Questions :

Q1. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.

Answer:  Inside the loop: If you use your right hand and curl your fingers in the direction of the clockwise current flow, your thumb will point towards the center of the loop. So, the direction of the magnetic field inside the loop is towards the center.

Outside the loop: Again, if you use your right hand and curl your fingers in the direction of the clockwise current flow, your thumb will now point away from the center of the loop. So, the direction of the magnetic field outside the loop is away from the center.
Q2. The magnetic field in a given region is uniform. Draw a diagram to represent it.

Answer :

3. Choose the correct option.
The magnetic field inside a long straight solenoid-carrying current
(a) is zero.
(b) decreases as we move towards its end.
(c) increases as we move towards its end.
(d) is the same at all points.

Answer :  (d) is the same at all points.

Inside a long straight solenoid carrying current, the magnetic field is uniform, and its strength is the same at all points along the axis of the solenoid. This is one of the unique characteristics of a well-designed solenoid.

Example 13.2
An electron enters a magnetic field at right angles to it, as shown in Fig. 13.14. The direction of force acting on the electron will be

       Fig 13.14

(a) to the right.
(b) to the left.
(c) out of the page.
(d) into the page.

Answer : (d) into the page .

The direction of force is perpendicular to the direction of magnetic field and current as given by Fleming’s left hand rule. Again, the direction of current is taken opposite to the direction of motion of electrons. The force is therefore directed into the page .

Internal Questions :

Q1. Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)
(a) mass                (b) speed
(c) velocity           (d) momentum

Answer :   (b) speed

(c) velocity

(d) momentum

When a proton moves freely in a magnetic field, its speed, velocity, and momentum can change due to the influence of the magnetic force on the charged particle. The magnetic force can alter the direction of the proton's motion, which will affect its velocity and momentum. However, the mass of the proton remains constant.

Q2. In Activity 13.7, how do we think the displacement of rod AB will be affected if (i) current in rod AB is increased; (ii) a stronger horse-shoe magnet is used; and (iii) length of the rod AB is increased ?

Answer :  (i) If the current in rod AB is increased : The displacement of rod AB will increase.

The greater the current flowing through the rod, the stronger the magnetic field produced around the rod. As a result, the interaction between the magnetic field of the rod and the magnetic field of the horseshoe magnet will be more pronounced, leading to a larger force on the rod and causing it to move further.

(ii) If a stronger horseshoe magnet is used : The displacement of rod AB will increase.

A stronger horseshoe magnet will produce a more intense magnetic field. This stronger magnetic field will exert a greater force on the current-carrying rod, leading to a larger displacement.

(iii) If the length of the rod AB is increased : The displacement of rod AB will increase.

A longer rod will experience a larger force when placed in the magnetic field. This is because there is more conductor for the magnetic field to interact with, resulting in a greater displacement.

Q3. A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) towards south        (b) towards east
(c) downward               (d) upward

Answer :  (d) upward

When a positively-charged particle (such as an alpha-particle) is projected towards the west and is deflected towards the north by a magnetic field, it implies that the magnetic field is acting perpendicular to both the initial velocity (west) and the direction of deflection (north). According to the right-hand rule for positive charges, the magnetic field points upward in this scenario.

Internal Questions :

Q1. State Fleming’s left-hand rule.

Answer : Fleming's left-hand rule helps you find the direction of the force on a current-carrying wire in a magnetic field.

Hold out your left hand with your thumb, forefinger, and middle finger at right angles to each other:

(i) Thumb represents the direction of the force (F).

(ii) Forefinger represents the direction of the current (I) in the wire.

(iii) Middle finger represents the direction of the magnetic field (B).

When you point your forefinger in the direction of the current and your middle finger in the direction of the magnetic field, your thumb will show you the direction of the force on the wire.

Q2. What is the principle of an electric motor?

Answer: An electric motor is a rotating device that converts electrical energy to mechanical energy.
Q3. What is the role of the split ring in an electric motor?

Answer : The split ring in an electric motor serves as a commutator, helping to change the direction of the electric current in the coil and enabling the motor to keep rotating continuously.

Internal Questions :

Q1. Explain different ways to induce current in a coil.

Answer : There are two simple ways to induce current in a coil:

(i) By moving the coil in a magnetic field: When a coil of wire moves through a magnetic field, the changing magnetic field induces a current in the coil.

(ii) By changing the magnetic field through the coil: If the magnetic field passing through the coil changes, even if the coil is stationary, it can still induce a current in the coil.

Internal Questions :

Q1. State the principle of an electric generator.

Answer: In an electric generator, mechanical energy is used to rotate a conductor in a magnetic field to produce electricity.

Q2. Name some sources of direct current.

Answer :  Some sources of direct current (DC) include batteries, solar cells, fuel cells, DC generators, rectifiers, DC power supplies, wind turbines, and certain hydroelectric generators.
Q3. Which sources produce alternating current?

Answer : Alternating current (AC) is produced by sources such as power plants, generators, and electrical grids. AC power is commonly used for residential, commercial, and industrial applications due to its ability to be easily transmitted over long distances
Q4. Choose the correct option.
A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each
(a) two revolutions (b) one revolution
(c) half revolution (d) one-fourth revolution

Answer :  (b) one revolution .

When a rectangular coil of copper wires is rotated in a magnetic field, the direction of the induced current changes once in each revolution.

Internal Questions :

Q1. Name two safety measures commonly used in electric circuits and appliances.

Answer: (i) Use of fuses or circuit breakers: Fuses and circuit breakers are safety devices used in electric circuits to protect against excessive current .

(ii) Grounding: Grounding is a safety measure that involves connecting electrical devices and appliances to the Earth using a ground wire.

Q2. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.

Answer: The electric oven requires 9.09 A to operate (2 kW ÷ 220 V). But the circuit can only handle up to 5 A. So, the oven won't work properly. The circuit's safety feature, like a fuse or circuit breaker, will likely cut off the power to prevent overloading and potential damage.
Q3. What precaution should be taken to avoid the overloading of domestic electric circuits ?

Answer: To avoid overloading domestic electric circuits:

(i)  Limit the use of too many appliances simultaneously.

(ii) Don't overload extension cords with high-power devices.

(iii) Unplug unused appliances.

(iv) Distribute heavy power users across different circuits.

(v) Check circuit ratings before connecting devices.        

(vi) Use energy-efficient appliances with lower power consumption.

 Class 10 Science Chapter 13 Magnetic Effects of Electic Current Exercise Questions and Answers :

Q1. Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire.
(b) The field consists of straight lines parallel to the wire.
(c) The field consists of radial lines originating from the wire.
(d) The field consists of concentric circles centred on the wire.

Answer :  (d) The field consists of concentric circles centred on the wire.

When a current flows through a long straight wire, the magnetic field around the wire forms concentric circles. The direction of the magnetic field lines can be determined using the right-hand rule: if you point your thumb in the direction of the current, the curling of your fingers shows the direction of the magnetic field lines around the wire.

Q2. The phenomenon of electromagnetic induction is
(a) the process of charging a body.
(b) the process of generating magnetic field due to a current passing through a coil.
(c) producing induced current in a coil due to relative motion between a magnet and the coil.
(d) the process of rotating a coil of an electric motor.

Answer : (c) producing induced current in a coil due to relative motion between a magnet and the coil.

Electromagnetic induction is the phenomenon where a changing magnetic field, or relative motion between a magnet and a coil, leads to the generation of an induced current in the coil. This principle is the basis for many applications, including generators, transformers, and various electrical devices.

Q3. The device used for producing electric current is called a
(a) generator.
(b) galvanometer.
(c) ammeter.
(d) motor.

Answer :  (a) generator.

A generator is a device used to produce electric current by converting mechanical energy into electrical energy. It operates based on the principle of electromagnetic induction, where the relative motion between a coil and a magnetic field induces an electric current in the coil. Generators are commonly used to generate electricity in power plants and various other applications.

Q4. The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.

Answer : (d) AC generator has slip rings while the DC generator has a commutator.

In an AC generator, the electricity is generated as alternating current, and the coil connections are made through slip rings. Slip rings allow the current to change direction with the rotation of the coil, resulting in an alternating current output.

In a DC generator, the electricity is generated as direct current, and the coil connections are made through a commutator. The commutator ensures that the current flows in one direction in the external circuit, resulting in a direct current output.

Q5. At the time of short circuit, the current in the circuit
(a) reduces substantially.
(b) does not change.
(c) increases heavily.
(d) vary continuously.

Answer :  (c) increases heavily.

During a short circuit, the low-resistance path causes a rapid surge in current, as there is little impedance to limit the flow. This can be dangerous and damaging.

Q6. State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with a green insulation is usually the live wire of an electric supply.

Answer : (a) False. An electric motor converts electrical energy into mechanical energy. It uses the principle of electromagnetic forces to produce mechanical motion.

(b) True. An electric generator works on the principle of electromagnetic induction. It converts mechanical energy into electrical energy by rotating a coil within a magnetic field.

(c) False. The field at the centre of a long circular coil carrying current will be nearly uniform and along the axis of the coil, not parallel straight lines.

(d) False. In most standard electrical systems, a wire with green insulation is used for grounding, not the live wire of an electric supply. The live wire is typically color-coded differently, such as black, red, or brown, depending on the country's electrical wiring code.

Q7. List three sources of magnetic fields.

Answer: Three sources of magnetic fields are:

(i) Permanent magnets: Materials such as iron, nickel, and cobalt possess inherent magnetic properties, creating a magnetic field around them.

(ii) Electric currents: Flowing electric currents generate magnetic fields according to Ampere's law, with the strength depending on the current magnitude and configuration.

(iii) Electromagnets: Temporary magnets created by wrapping a coil of wire around a ferromagnetic core and passing an electric current through the coil, producing a magnetic field.

Q8. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current–carrying solenoid with the help of a bar magnet? Explain.

Answer: A solenoid behaves like a magnet due to the magnetic field generated by the current flowing through its coil. The magnetic field lines produced by the solenoid resemble those of a bar magnet. The north and south poles of a solenoid can be determined using a bar magnet. When one end of a bar magnet is brought close to the solenoid, it will either attract or repel the end of the bar magnet, indicating the opposite pole of the solenoid.
Q9. When is the force experienced by a current–carrying conductor placed in a magnetic field largest?

Answer: The force experienced by a current-carrying conductor placed in a magnetic field is largest when the direction of the current is perpendicular to the direction of the magnetic field. This is in accordance with the right-hand rule for the force on a current-carrying conductor.
Q10. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?

 Answer: Based on the given scenario, the direction of the magnetic field is perpendicular to both the motion of the electron beam (from the back wall to the front wall) and the deflection of the beam to the right side. Thus, the magnetic field is directed towards the ceiling.
Q11.What is the function of a split ring in an electric motor ?

Answer : The function of a split ring, also known as a commutator, in an electric motor is to reverse the direction of current in the coil every half-turn, enabling the motor to rotate continuously.
Q12. Name some devices in which electric motors are used.

Answer: Some devices are :  (i) Electric fans    (ii) Washing machines   (iii) Vacuum cleaners  (iv) Refrigerators  (v) Air conditioners

Q13. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil ?

Answer: (i) When the bar magnet is pushed into the coil, the changing magnetic field induces a current in the coil. This current causes a deflection in the galvanometer.

(ii) When the bar magnet is withdrawn from inside the coil, a current is again induced, but with opposite polarity, resulting in a deflection in the galvanometer in the opposite direction.

(iii) If the bar magnet is held stationary inside the coil, no relative motion occurs, and there is no change in magnetic flux. As a result, no current is induced, and the galvanometer shows no deflection.

Q14. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.

Answer: Yes, if the current in coil A is changed, some current will be induced in coil B. This is due to electromagnetic induction, as the changing magnetic field produced by the changing current in coil A induces an electromotive force (EMF) in coil B, resulting in an induced current.
Q15. 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.

Answer :   (i) To determine the direction of the magnetic field produced around a straight conductor carrying current, use the right-hand rule. If you wrap your right hand around the conductor with your thumb pointing in the direction of the current, your fingers will curl in the direction of the magnetic field lines.

(ii) To determine the direction of the force experienced by a current-carrying straight conductor placed in a magnetic field (perpendicular to it), use the left-hand rule. If you point your left-hand thumb in the direction of the current and extend your fingers in the direction of the magnetic field, your palm will face the direction of the force experienced by the conductor.

(iii) To determine the direction of the current induced in a coil due to its rotation in a magnetic field, use the right-hand rule for electromagnetic induction. If you point your right-hand thumb in the direction of the rotation of the coil, the induced current in the coil will flow in the direction of your curled fingers.

Q17. When does an electric short circuit occur?

Answer: An electric short circuit occurs when there is a low-resistance path or direct connection between the live and neutral wires, bypassing the intended load, leading to excessive current flow and potential hazards.
Q18. What is the function of an earth wire? Why is it necessary to earth metallic appliances ?

Answer: The function of an earth wire is to provide a safe path for electric current to flow into the ground during faults or malfunctions.

It is necessary to earth metallic appliances for electrical safety, protecting against electric shocks, diverting fault currents, and preventing damage to equipment and structures.