VERY SHORT ANSWER QUESTIONS CARRYING 1 MARK WITH ANSWER
Q.1 A straight wire carrying electric current is moving out of plane of paper and is perpendicular to it. What is the direction and type of induced magnetic field lines ?
Answer: Induced magnetic field lines will be in the form of concentric circles in the plane of paper.
Q.2 How can it be shown that magnetic field exist around a wire carrying current?
Answer: By using magnetic compass which shows deflection
Q.3 How can a solenoid be used to magnetise a steel bar.
Answer: By inserting the steel bar inside the solenoid and switching on electric current
Q.4 Why can’t two magnetic field lines ever intersect?
Answer: If so then at the point of intersection there will be two different directions of magnetic field which is not possible.
Q.5 Can a 5 A fuse be used in wire carrying 15 A current? Why?
Answer: No, because it would then be ineffective in controlling the amount of current flowing.
Q.6 Give the factors that affect strength of magnetic field at a point due to a straight conductor
carrying current.
Answer: Magnitude of electric current, perpendicular distance between that point and conductor.
Q.7 Where do we connect a fuse: with live wire or with neutral wire?
Answer: It is always connected with live wire.
Q.8 Give two uses of electromagnets.
Answer: (i) It is used in cranes for lifting heavy loads. (ii) used in electric bells.
Q.9 Name any two devices which use permanent magnets.
Answer: Loudspeakers, Galvanometer, voltmeter
Q.10 Draw the magnetic field lines representing uniform magnetic field.
Answer: Equidistant parallel straight lines
SHORT ANSWER QUESTIONS CARRYING 2 MARK WITH ANSWER
Q.11 A current-carrying straight conductor is placed in the east-west direction. What will be the direction of the force experienced by this conductor due to earth’s magnetic field? How will this force get affected on?
(a) reversing the direction of flow of current
(a) By reversing the direction of current, the direction of I will be reversed i.e. vertically downwards.
(b) The magnitude of the force is doubled
Q.12 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
Answer: When a conductor carrying current is placed perpendicular to the direction of magnetic field, the force 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
Q.13 Why is the earth pin thicker and longer than the live and the neutral pins?
Answer. It is thicker so that it does not enter into the live or neutral sockets. It is made longer so that it gets connected to the earth terminal earlier than the live and neutral pins. This ensures the safety of the user.
Q.14 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 inside the coil? (iii) Held stationary inside the coil?
Answer. (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
eft opposite to that in case one).
( iii) As it is stationary no change in magnetic flux linked with coil, so galvanometer shows no deflection
3 marks Questions and answer :Chapter: Magnetic Effects of Currents
1. Why does a current carrying conductor kept in a magnetic field experience force? On what factors does the direction of this force depend? Name and state the rule used for determination of direction of this force.
Answer: Force on a conductor carrying current in a magnetic field :-
A.M. Ampere suggested that if a current carrying conductor produces a magnetic field and exerts a
force on a magnet, then a magnet should also exerts a force on a current carrying conductor.
Eg :- If an aluminum rod is suspended horizontally by a wire between the poles of a horse shoe
magnet and current is passed through the wire, then the aluminum rod is displaced. If the direction of
current is reversed, the direction of displacement is also reversed. The force exerted is maximum if
the conductor is perpendicular to the magnetic field.
Fleming’s Left Hand Rule :-
The direction of force (motion) of a current carrying conductor in a magnetic field is given by
Fleming’s Left Hand Rule.
Overloading is caused due to increase in voltage, or if the live wire and neutral wire comes in contact or if too many appliances are connected to a single socket. It results in overheating of the wires and can cause damage to the circuit and appliances.
c) Short circuit :-
Short circuit is caused when the live wire and neutral wire comes in contact and the current suddenly increases in the circuit. It causes spark, fire and damage to the circuit and appliances.
3. Explain Direct and Alternating current
Answer:
(a) Direct current (DC) :- A current that always flows in one direction only is called direct current. The current we get from a battery is a direct current.
(b) Alternating current (AC) :- A current that reverses its direction periodically is called alternating current. Most power stations in our country produce alternating current. AC changes direction every 1/100 second and its frequency is 50 Hertz (Hz). One advantage of AC over DC is that it can be transmitted over long distances without much loss of energy
4. Draw the pattern of magnetic field lines of a current carrying solenoid. What does the pattern of
field lines inside the solenoid indicate? Write one application of magnetic field of current carrying
solenoid. Figure 13.10 (Page No.229 NCERT Text Book)
Answer: Pattern of magnetic field lines It indicates that the magnetic field is the same at all points
inside the solenoid
Application- For making an electromagnet
5 marks Questions & Answers of Magnetic Effects of Electric Currents
1. Explain with an experiment principle of Electromagnetic induction? Which law will gives the
direction of electric current?
Answer: The motion of a magnet with respect to a coil or a change in the magnetic field induce a
potential difference in the coil and produces induced current. This is called electromagnetic
induction.
i) Motion of a magnet with respect to a coil produces induced current :-
If a magnet is moved towards or away from a coil of wire connected to a galvanometer, the
galvanometer needle shows a deflection. This shows that current is induced in the coil due to the
motion of the magnet.
Change in magnetic field produces induced current :-
Take two coils of wires wound around a cylindrical paper roll. Connect one coil to a battery and the
other coil to a galvanometer. If current is passed through the first coil, the galvanometer needle shows
a deflection in the second coil. If the current is disconnected, the needle moves in the opposite
direction. This shows that current is induced due to change in magnetic field.
Fleming’s Right Hand Rule :-
The direction of induced current is given by Fleming’s Right Hand Rule.
It states that ‘ If the thumb, fore finger and middle finger of the right hand is held perpendicular to
each other such that the thumb points in the direction of motion of the conductor, the fore finger
points in the direction of the magnetic field, then the middle finger shows the direction of induced
current ’.
2. Explain Domestic electric circuit?
Answer: Electric power to homes is supplied through the mains. It has two wires. One is a live wire
(positive wire) with red insulation and the other is a neutral wire (negative wire) with black insulation.
The potential difference between the two wires is 220V. The earth wire with green insulation is
connected to a metal plate kept in the ground.
Two separate circuits are used. One is of 15A for appliances with high power rating like gysers, air
conditioners etc. The other is of 5A for fans, bulbs etc. The different appliances are connected in
parallel so that every appliance gets equal voltage and even if one is switched off the others are not
affected.
The appliances having metallic body like electric iron, refrigerators etc., their metallic body is
connected to the earth wire so that if there is leakage of current, it passes to the earth and prevents
electric shock
3. Explain the meaning of the word ‘electromagnetic’ and ‘induction’ in the term electromagnetic
induction. On what factors does the value of induced current produced in a circuit depend? Name and state the rule used for determination of direction of induced current. State one practical application of this phenomenon in every day life.
Answer: Power can be transmitted over long distances without much loss of energy.
Q.1 A straight wire carrying electric current is moving out of plane of paper and is perpendicular to it. What is the direction and type of induced magnetic field lines ?
Answer: Induced magnetic field lines will be in the form of concentric circles in the plane of paper.
Q.2 How can it be shown that magnetic field exist around a wire carrying current?
Answer: By using magnetic compass which shows deflection
Q.3 How can a solenoid be used to magnetise a steel bar.
Answer: By inserting the steel bar inside the solenoid and switching on electric current
Q.4 Why can’t two magnetic field lines ever intersect?
Answer: If so then at the point of intersection there will be two different directions of magnetic field which is not possible.
Q.5 Can a 5 A fuse be used in wire carrying 15 A current? Why?
Answer: No, because it would then be ineffective in controlling the amount of current flowing.
Q.6 Give the factors that affect strength of magnetic field at a point due to a straight conductor
carrying current.
Answer: Magnitude of electric current, perpendicular distance between that point and conductor.
Q.7 Where do we connect a fuse: with live wire or with neutral wire?
Answer: It is always connected with live wire.
Q.8 Give two uses of electromagnets.
Answer: (i) It is used in cranes for lifting heavy loads. (ii) used in electric bells.
Q.9 Name any two devices which use permanent magnets.
Answer: Loudspeakers, Galvanometer, voltmeter
Q.10 Draw the magnetic field lines representing uniform magnetic field.
Answer: Equidistant parallel straight lines
SHORT ANSWER QUESTIONS CARRYING 2 MARK WITH ANSWER
Q.11 A current-carrying straight conductor is placed in the east-west direction. What will be the direction of the force experienced by this conductor due to earth’s magnetic field? How will this force get affected on?
(a) reversing the direction of flow of current
(b) doubling the magnitude of current.
Answer. The direction of earth’s magnetic field is from G-south to G-north. Let current is from west to east. Therefore force is vertically upwards.
Answer. The direction of earth’s magnetic field is from G-south to G-north. Let current is from west to east. Therefore force is vertically upwards.
(a) By reversing the direction of current, the direction of I will be reversed i.e. vertically downwards.
(b) The magnitude of the force is doubled
Q.12 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
Answer: When a conductor carrying current is placed perpendicular to the direction of magnetic field, the force 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
Q.13 Why is the earth pin thicker and longer than the live and the neutral pins?
Answer. It is thicker so that it does not enter into the live or neutral sockets. It is made longer so that it gets connected to the earth terminal earlier than the live and neutral pins. This ensures the safety of the user.
Q.14 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 inside the coil? (iii) Held stationary inside the coil?
Answer. (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
eft opposite to that in case one).
( iii) As it is stationary no change in magnetic flux linked with coil, so galvanometer shows no deflection
3 marks Questions and answer :Chapter: Magnetic Effects of Currents
1. Why does a current carrying conductor kept in a magnetic field experience force? On what factors does the direction of this force depend? Name and state the rule used for determination of direction of this force.
Answer: Force on a conductor carrying current in a magnetic field :-
A.M. Ampere suggested that if a current carrying conductor produces a magnetic field and exerts a
force on a magnet, then a magnet should also exerts a force on a current carrying conductor.
Eg :- If an aluminum rod is suspended horizontally by a wire between the poles of a horse shoe
magnet and current is passed through the wire, then the aluminum rod is displaced. If the direction of
current is reversed, the direction of displacement is also reversed. The force exerted is maximum if
the conductor is perpendicular to the magnetic field.
Fleming’s Left Hand Rule :-
The direction of force (motion) of a current carrying conductor in a magnetic field is given by
Fleming’s Left Hand Rule.
It states that ‘ If we hold the thumb, fore finger and middle finger of the left hand perpendicular to
each other such that the fore finger points in the direction of magnetic field, the middle finger points
in the direction of current, then the thumb shows the direction of force (motion) of the conductor
2. Explain a) Electric fuse b) Overloading c) Short circuit
Answer:
(a) Electric fuse :-
Electric fuse is a safety device used in electric circuits to protect the circuit and appliances from damage due to overloading and short circuit. It is a wire having high resistance and low melting point.
each other such that the fore finger points in the direction of magnetic field, the middle finger points
in the direction of current, then the thumb shows the direction of force (motion) of the conductor
2. Explain a) Electric fuse b) Overloading c) Short circuit
Answer:
(a) Electric fuse :-
Electric fuse is a safety device used in electric circuits to protect the circuit and appliances from damage due to overloading and short circuit. It is a wire having high resistance and low melting point.
If excess current flows through the circuit, the fuse wire melts and breaks the circuit.
Fuse wire is made of a metal or an alloy of metals like lead, tin, aluminium and copper(solder is an alloy. Fuse wire is connected in series with the live wire.
(b) Overloading :-
(b) Overloading :-
Overloading is caused due to increase in voltage, or if the live wire and neutral wire comes in contact or if too many appliances are connected to a single socket. It results in overheating of the wires and can cause damage to the circuit and appliances.
c) Short circuit :-
Short circuit is caused when the live wire and neutral wire comes in contact and the current suddenly increases in the circuit. It causes spark, fire and damage to the circuit and appliances.
3. Explain Direct and Alternating current
Answer:
(a) Direct current (DC) :- A current that always flows in one direction only is called direct current. The current we get from a battery is a direct current.
(b) Alternating current (AC) :- A current that reverses its direction periodically is called alternating current. Most power stations in our country produce alternating current. AC changes direction every 1/100 second and its frequency is 50 Hertz (Hz). One advantage of AC over DC is that it can be transmitted over long distances without much loss of energy
4. Draw the pattern of magnetic field lines of a current carrying solenoid. What does the pattern of
field lines inside the solenoid indicate? Write one application of magnetic field of current carrying
solenoid. Figure 13.10 (Page No.229 NCERT Text Book)
Answer: Pattern of magnetic field lines It indicates that the magnetic field is the same at all points
inside the solenoid
Application- For making an electromagnet
5 marks Questions & Answers of Magnetic Effects of Electric Currents
1. Explain with an experiment principle of Electromagnetic induction? Which law will gives the
direction of electric current?
Answer: The motion of a magnet with respect to a coil or a change in the magnetic field induce a
potential difference in the coil and produces induced current. This is called electromagnetic
induction.
i) Motion of a magnet with respect to a coil produces induced current :-
If a magnet is moved towards or away from a coil of wire connected to a galvanometer, the
galvanometer needle shows a deflection. This shows that current is induced in the coil due to the
motion of the magnet.
Change in magnetic field produces induced current :-
Take two coils of wires wound around a cylindrical paper roll. Connect one coil to a battery and the
other coil to a galvanometer. If current is passed through the first coil, the galvanometer needle shows
a deflection in the second coil. If the current is disconnected, the needle moves in the opposite
direction. This shows that current is induced due to change in magnetic field.
Fleming’s Right Hand Rule :-
The direction of induced current is given by Fleming’s Right Hand Rule.
It states that ‘ If the thumb, fore finger and middle finger of the right hand is held perpendicular to
each other such that the thumb points in the direction of motion of the conductor, the fore finger
points in the direction of the magnetic field, then the middle finger shows the direction of induced
current ’.
2. Explain Domestic electric circuit?
Answer: Electric power to homes is supplied through the mains. It has two wires. One is a live wire
(positive wire) with red insulation and the other is a neutral wire (negative wire) with black insulation.
The potential difference between the two wires is 220V. The earth wire with green insulation is
connected to a metal plate kept in the ground.
Two separate circuits are used. One is of 15A for appliances with high power rating like gysers, air
conditioners etc. The other is of 5A for fans, bulbs etc. The different appliances are connected in
parallel so that every appliance gets equal voltage and even if one is switched off the others are not
affected.
The appliances having metallic body like electric iron, refrigerators etc., their metallic body is
connected to the earth wire so that if there is leakage of current, it passes to the earth and prevents
electric shock
3. Explain the meaning of the word ‘electromagnetic’ and ‘induction’ in the term electromagnetic
induction. On what factors does the value of induced current produced in a circuit depend? Name and state the rule used for determination of direction of induced current. State one practical application of this phenomenon in every day life.
Answer: Power can be transmitted over long distances without much loss of energy.
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