1. 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’s.
d. Relative strength of magnetic field lines is given by degree of closeness of the filed lines
2.Why don’t two magnetic lines of force intersect each other?
Ans. No, two magnetic field lines can ever intersect each other. If they do, then it would mean that at the point of intersection there are two directions of magnetic field, which is not possible.
3.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
4. 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
5.What is the role of the split ring in an electric motor?
Ans. In electric motor, the split ring acts as commutator. Due to its action, the direction of current flowing in motor coil reverses after half turn, giving rise to a continuous rotation of the coil and the axle
6.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.
7.Name some sources of direct current.
Ans. Some sources of direct current are a cell, a battery and a D.C. generator
8.Which sources produce alternating current?
Ans. A.C. generator and common inverter used in houses for emergency power supply produce alternating current
9.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
10.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.
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 connectd with positive terminal behaves like South Pole and the end connected with negative terminal behaves as North Pole
11. When is the force experienced by a current-carrying conductor placed in magnetic field largest?
Ans. The force experienced by a current carrying conductor placed in a magnetic field is largest when the conductor is placed with its length in a direction perpendicular to that of magnetic field
12. When does an electric short circuit occurs?
Ans. If either the insulation of wires used in an electric circuit is damaged or there is a fault in the appliances, live wire and neutral wire may come in direct contact. As a result, the current in the circuit abruptly rises and short circuiting occurs.
13.Electric appliance like electric-press, toaster, fans etc are connected to electric mains through three-pin plug. Why?
Ans. Electric appliances are connected to three pin plug because heavy appliances require earth wire, so that in case of leakage of any current it goes to earth and user will not get shock.
14.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) W ashing 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.
(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.
15. (a) What is short circuiting?
(b) What is overloading? How can you avoid overloading?
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.
16.(a) Distinguish between A.C and D.C?
(b) Which source produces alternating current?
Ans. 18. (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
19.. 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) W hen a bar magnet is pushed into the coil of insulated copper wire connected to a galvanometer, galvanometer gives a deflection towards left.
(ii) W hen 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.
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’s.
d. Relative strength of magnetic field lines is given by degree of closeness of the filed lines
2.Why don’t two magnetic lines of force intersect each other?
Ans. No, two magnetic field lines can ever intersect each other. If they do, then it would mean that at the point of intersection there are two directions of magnetic field, which is not possible.
3.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
4. 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
5.What is the role of the split ring in an electric motor?
Ans. In electric motor, the split ring acts as commutator. Due to its action, the direction of current flowing in motor coil reverses after half turn, giving rise to a continuous rotation of the coil and the axle
6.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.
7.Name some sources of direct current.
Ans. Some sources of direct current are a cell, a battery and a D.C. generator
8.Which sources produce alternating current?
Ans. A.C. generator and common inverter used in houses for emergency power supply produce alternating current
9.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
10.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.
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 connectd with positive terminal behaves like South Pole and the end connected with negative terminal behaves as North Pole
11. When is the force experienced by a current-carrying conductor placed in magnetic field largest?
Ans. The force experienced by a current carrying conductor placed in a magnetic field is largest when the conductor is placed with its length in a direction perpendicular to that of magnetic field
12. When does an electric short circuit occurs?
Ans. If either the insulation of wires used in an electric circuit is damaged or there is a fault in the appliances, live wire and neutral wire may come in direct contact. As a result, the current in the circuit abruptly rises and short circuiting occurs.
13.Electric appliance like electric-press, toaster, fans etc are connected to electric mains through three-pin plug. Why?
Ans. Electric appliances are connected to three pin plug because heavy appliances require earth wire, so that in case of leakage of any current it goes to earth and user will not get shock.
14.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) W ashing 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.
(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.
15. (a) What is short circuiting?
(b) What is overloading? How can you avoid overloading?
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.
16.(a) Distinguish between A.C and D.C?
(b) Which source produces alternating current?
Ans. 18. (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
19.. 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) W hen a bar magnet is pushed into the coil of insulated copper wire connected to a galvanometer, galvanometer gives a deflection towards left.
(ii) W hen 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.
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