Important Questions for CBSE Class 10 Science Chapter 13 - Magnetic Effects of Electric Current 3 Mark Question

CBSE Class 10 Science Chapter-13 Magnetic Effects of Electric Current – Free PDF Download

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CBSE Class 10 Science Chapter-13 Magnetic Effects of Electric Current Important Questions

3 Mark Questions

1. What is the function of an earth wire? Why is if necessary to earth metallic casing of electric appliance?
Ans. Earth will acts as a safety device. When live wire touches the metallic appliance then electric current flows through castling to the earth instead of human body and thus we prevent ourselves from getting shock. It is necessary to earth metallic casing of the appliance because it saved electrical appliance from burning and prevent us from electric shock.

2. We know a current carrying conductor placed in a magnetic field experiences a force due to which the conductor moves. How do we think the rod displaces if-(a) current in rod is increased
(b) a stronger horse shoe is inserted
(c) length of the rod is increased.
Ans. Force acting on current carrying conductor
F=BIL
(a) When I increase, F also increases hence displacement of the rod increases.
(b) When a stronger horse shoe magnet is inserted, magnetic field B increases. So force F increase. Hence displacement increases.
(c) When I increase, force increases and hence displacement increases.

3. What is the principle of electric motor? State the function of
(i) split ring
(ii) field magnet used in electric motor.
Ans. Electric motor works on the principle that a current carrying conductor placed perpendicular to a magnetic field experiences a force.
(i) Split ring – It reverses the dissection of current in the armature and thus direction of force is also reserved. As a result dc motor continues to rotate in same direction.
(ii) Field magnet – It provided strong magnetic field.

4. State three factor on which magnetic field produced by a current carrying solenoid depends.
Ans. (1) The strength of the current flowing through the solenoid.
(2) No. of turns of the wire of the solenoid.
(3) Nature of the material inside solenoid.

5. What is a solenoid? Draw magnetic field lines showing the magnetic field inside and outside the current carrying solenoid?

Ans.
A solenoid is a coil of many turns of insulated copper wire closely wound in the shape of a ring.

6. (a) Name four appliances wherein an electric motor is used as an important component. In what respect it is different from generator?
(b) Define the terms used in the generator
(i) armature
(ii) slip rings
(iii) brushes
Ans. (a) The four appliances which have electric motor inside them are
(i) Mixers (ii) Washing machine (iii)Refrigerators (iv) Blenders
(b) (i) Armature – Armature is a coil of large number of turns of insulated copper wire wound over a soft iron core.
(ii) Slip rings- Slip Rings one two rings made up of brass which rotates along with the coil.
(iii) Brushes- Brushes are made up of carbon which are pressed against the slip rings and are connected to external circuit where output is obtained.

7. (a) What is the standard colour code followed for
(i) live
(ii) neutral and
(iii) earth wires used in electric circuits?
(b) Which part of an electric appliance is earthed and why?
Ans. (a) The standard colour code for
Live wire – Red
Neutral – Black
Earth – Green respectively.
(b) The metallic case of an electrical appliance is earthed because metals are good conductors of electricity and in case if current exceeds i.e. live wire touches the metallic case of an appliance and then due to earthing all the excess amount of current flows down to the earth and we prevent ourselves from an electric shock.

8. (a) What is short circuiting?
Ans. (a) Short circuiting means when live wire and the neutral wires come in contact with each other. Due to this resistance of the circuit becomes very small and huge amount of current flows through the circuit which is turn produces more heat which can cause fire.
(b) Overloading means large amount of current flows in the circuit. It can happen when many electrical appliances of high power ratings are connected in a single socket. It can be avoided by the following methods:
(i)Not use too many appliance is a single socket
(ii)To apply preventive methods of short circuiting.

9. Define electromagnetic induction? Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in the coil B? Explain.
Ans. Electromagnetic induction means the production of induced current in a closed coil due to the change in the magnetic field. When current in coil A is changed, magnetic flux sets up around coil A due to which some magnetic field set up in the coil B thus some induced current flow through coil B due to which galvanometer deflects.

10. Why does a current carrying conductor kept in a magnetic field experience force? What is the direction of force acting on the conductor?
Ans. A current carrying coil contains charged particles which experiences a force (Bqv). The total
force experienced by the charged particle is equal to the force experienced by the conductor which is perpendicular to both the magnetic field and the direction of current in the conductor.

11. (a) Distinguish between A.C and D.C?
(b) Which source produces alternating current?
Ans.

12. (a) Define the term current rating of an electric fuse?
(b) Name the material used to make electric fuse?
(c) Name two safety measure commonly used in electric circuit and appliances?
Ans. (a)The maximum amount of current that can be passed through the fuse wire without melting it.
(b) Copper or alloy of lead acid tin.
(c) Electric fuses and earth wire.

13. Why does a compass needle get deflected when brought near a bar magnet?
Ans. The compass needle is small bar magnet. When a compass needle is brought near a bar magnet then due to repulsive force between unlike poles and attraction between unlike poles, the compass needle is deflected and settle in the direction of net magnetic field.

14. List the properties of magnetic lines of force.
Ans. Properties of magnetic field lines of force as follows:
a. Outside a magnet, the field lines are directed from N-pole of magnet towards S-pole and inside the magnet lines are directed form S-pole to N-pole.
b. Magnetic field lines are closed curves.
c. No two magnetic field lines intersect each other.
d. Relative strength of magnetic field lines is given by degree of closeness of the filed lines.

15. In activity 13.7, how do we think the displacement of rod AB will be affected if
(i) current is rod AB is increased,
(ii) a stronger horse shoe magnet is used, and
(iii) length of the rod AB is increased?
Ans. (i) O increasing the current in rod AB its displacement will increase.
(ii) If stronger horse-shoe magnet is used then the displacement of rod AB will increase.
(iii) If length of the rod is increased, force acting on it will increase and hence, displacement of the rod increases.

16. State Fleming’s left-hand rule.
Ans. Fleming’s left hand rule states that stretch the forefinger, the central finger and the thumb of your left hand mutually perpendicular to each other. If the forefinger shows the direction of the magnetic field and central finger that of the current, then the thumb will point towards the direction of motion of the conductor.

17. What is the principle of an electric motor?
Ans. An electric motor is based on the principle that the current carrying conductor experiences a force when placed in a magnetic field. If the direction of the magnetic field and that of the current are mutually perpendicular, then the direction of the force is given by Fleming’s left-hand rule.

18. Explain different ways to induce current in a coil.
Ans. Different ways to induce current in a coil are as follows:
(a) If a magnetic field is changed around a coil then an induced current is set up in the coil.
(b) If a coil is moved in magnetic field, then again an induced current is set up in the coil.
(c) If a coil is rotated in a uniform magnetic field

19. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220V) that has a current rating of 5.A. What result do you expect? Explain.
Ans. Power rating of electric oven (P) = 2 kW = 2000 W
Current drawn (I) = P/V = 2000/220 = 9.09 A.
As the current rating of domestic electric circuit is only 5A the oven draws a current of 9.09 A. Which is more than the current rating; hence the circuit will be damaged due to overheating/overloading.

20. What precaution should be taken to avoid the overloading of domestic electric circuit?
Ans. We should take following precaution to avoid the overloading of domestic electric circuit:
(a) Two separate circuits should be used, one of 5A current rating of bulbs, fans, tubes etc. and the other 15 A current rating for appliances with higher current rating such as geysers, air coolers, electric iron, electric stoves etc.
(b) Too many appliances should never be connected to a single socket.
(c) A fuse of appropriate current rating should be used with the electric circuit.

21. List three methods of producing magnetic field.
Ans. Three methods of producing magnetic fields are as follows:
(a) Magnetic field can be produced by placing a permanent magnet or a horse-shoe magnet at the place, where magnetic field is required.
(b) Magnetic field is produced around a current carrying straight conductor or a current carrying coil.
(c) A very good method to produce magnetic field is due to flow of current in a solenoid.

22. How does a solenoid behave like a magnet? Can you determines the north and south poles of a current carrying solenoid with the help of a bar magnet? Explain.
Ans. When current is passed through a solenoid coil, magnetic field is produced due to presence of turns in same direction. As a result, the resultant magnetic field is very strong and uniform.
Solenoid behaves like a strong bar magnet. We can determine the poles of magnet formed by solenoid. The end of solenoid connected with positive terminal behaves like South Pole and the end connected with negative terminal behaves as North Pole.

23. Imagine that you are sitting in 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?
Ans. An electron beam moving horizontally from back wall towards the front wall is equivalent to a current flowing in the opposite direction. The deflection of electron beam as seen by the observer is to his right side. On applying Fleming’s left-hand rule we find that the magnetic field is acting in vertically downward direction.

24. 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?
Ans. (i)When a bar magnet is pushed into the coil of insulated copper wire connected to a galvanometer, galvanometer gives a deflection towards left.
(ii) When the bar magnet is withdrawn from inside the coil, again an induced current is set in coil that deflect the galvanometer towards right.
(iii) If the bar magnet is held stationary inside the coil, then no induced current is set and galvanometer does not show any deflection.

25. Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
Ans. Yes, a current is induced in the coil B.
When the current in the coil A is changed, the magnetic field associated with it also changes. As coil B is placed close to A, hence magnetic field lines around this coil also change. Due to change in magnetic field lines associated with coil B, an induced current is also induced in it.

26. State the rule to determine the direction of a
(i) magnetic field produced around a straight current carrying conductor
(ii) force experienced by a current carrying straight conductor
(iii) current induced in a coil due to its rotation in a magnetic field.
Ans. (i) To know the direction of magnetic field produced around a straight conductor we make use “Right hand thumb Rule”.
(ii) To find the direction of force experienced by a current carrying straight conductor placed in a
magnetic field we make use “Fleming’s left hand rule”.
(iii) For finding the direction of current induced in a coil we use “Fleming’s right hand rule”.

27. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Ans. The earth wires functions as a safety measure, especially for those appliances that have a metallic body, like heater, electric, press, room cooler etc. The metallic body of the appliance is connected to the earth wire, which provides a low resistance conducting path for electric current. It ensures that any leakage of current to the metallic body of an appliance keeps it potential same as of earth. As a result, the user would not get severe electric shock, even if he touches the body of appliance.

28. A coil of insulated copper wire is connected to a galvanometer. What would happen if a bar magnet Is.
(i) Pushed into the coil?
(ii) Withdrawn from Side the coil?
(iii) Held stationary inside the coil?
Ans. (i) Due to change in magnetic flux linked with coil, the galvanometer shows deflection (say towards right).
(ii) Due to change in magnetic flux linked with coil, the galvanometer shows deflection (say towards left opposite to that in case one).
(iii) As it is stationary no change in magnetic flux linked with coil, so galvanometer shows no deflection.

29. An electron enters a magnetic field at right angles to it as shown in fig. The direction of the force acting on the electron will be:
(a) to the right (b) to the left (c) out of the page (d) into the page

Ans. When a conductor carrying current is placed perpendicular to the direction of magnetic field, the acting on it is given by Fleming’s left hand rule. Since the direction of current is the same as that of the motion of a positive charge, the direction of force acting on it when moving perpendicular to the direction of magnetic field is the same as that acting on a current-carrying conductor placed perpendicular to the direction of magnetic field. Obviously, the force acting on an electron is opposite to that. Therefore, in this case it is into the page.

30. Consider a circular wire lying in the plane of the table and the direction current in it is antilock wise.
(i) Draw the magnetic field lines produced around it.
(ii) Why does magnetic field at the center of current carrying circular loop appear straight? Explain with diagram.

Ans. (i)

(ii)
Because of large curvature of magnetic field lines at centre.

31. If we place a compass needle near straight conductor carrying current (a)What happens to the deflection of the compass needle if the direction of current reversed. Is (b)What change will you notice in the compass needle if it is moved away from conductor but the current through the conductor remains the same?
Ans. (a) Direction of deflection will reverse
(b) Deflection will decrease

32. A magnet is moving towards a coil as shown in figure.

(1) Which phenomenon is shown in figure.

(2) Which physical quantity is between magnet and coil? set up in the coil when there is a relative motion
(3) What may be the cause of production of that physical quantity?
Ans. (1) Electromagnetic induction
(2) Induced current
(3) Change in magnetic lines of forces through coil

33. Suppose your science teacher asks you to demonstrate the phenomena of EMI with following materials:
(a)Two different coils land 2 of copper wire having large no. of turns 50 and 100 respectively.
(b) A non conducting cylinder.
(c)A battery
(d) A plug key
(e) A galvanometer
(i) Draw a labeled diagram of your demonstration setup.
(ii)How will you prove the phenomena of EMI.
Ans. (i)

(ii)
When key is closed, there is deflection in galvanometer.