Chapter 12. Magnetic Effects of Electric Current

Class 10 Science Chapter 12. Magnetic Effects of Electric Current 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.

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. 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.

Q3. 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 .]