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Q. Explain the field lines around a current-carrying Circular Loop.
Ans. At every point of a current-carrying circular loop, the concentric circles
representing the magnetic field around it and as the magnetic field
produced by a current-carrying wire depends inversely on the distance from
it so the concentric circles would become larger and larger as we move
away from the wire. By the time we reach at the centre of the circular loop,
the arcs of these big circles would appear as straight lines.
Every point on the wire carrying current would give rise to the
magnetic field appearing as straight lines at the center of the loop. By
applying the right hand rule, it is easy to check that every section of the
wire contributes to the magnetic field lines in the same direction within the
loop.
Q. What is the effect of the number of turns of wire in a circular loop on the
magnetic field?
Ans. As the magnetic field produced by a current-carrying wire at a given
point depends directly on the current passing through it. Therefore, if there
is a circular coil having n turns, the field produced is n times as large as
that produced by a single turn. This is because the current in each circular
turn has the same direction, and the field due to each turn then just adds
up.
Q. What is solenoid?
Ans. A coil of many circular turns of insulated copper wire wrapped closely
in the shape of a cylinder is called a solenoid.
Q. Draw magnetic field lines around a current-carrying solenoid.
Ans.
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Q. Explain the magnetic field lines around a current-carrying solenoid.
Ans. The pattern of the magnetic field lines around a current-carrying
solenoid is similar to the magnetic field lines produced by a bar magnet. In
fact, one end of the solenoid behaves as a magnetic north pole, while the
other behaves as the south pole. The field lines inside the solenoid are in
the form of parallel straight lines. This indicates that the magnetic field is
the same at all points inside the solenoid. That is, the field is uniform inside
the solenoid.
Q. What is electromagnet?
Ans. A strong magnetic field produced inside a solenoid can be used to
magnetise a piece of magnetic material, like soft iron, when placed inside
the coil. The magnet so formed is called an electromagnet.
Q. 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.
Ans.
The direction of the magnetic field inside the loop is downward and
the direction of the magnetic field outside the loop is upward.
Q. The magnetic field in a given region is uniform. Draw a diagram to
represent it.
Ans. If the magnetic field in a given region is uniform the field lines must be
parallel lines and in the same direction. Diagram for the same is below:-
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Q. Choose the correct option.
The magnetic field inside a long straight solenoid-carrying current.
Ans. (d) is the same at all points.
Q. Explain the force on a current carrying conductor in a magnetic field.
Ans. An electric current flowing through a conductor produces a magnetic
field. The field so produced exerts a force on a magnet placed in the vicinity
of the conductor. French scientist Andre Marie Ampere suggested that the
magnet must also exert an equal and opposite force on the current-carrying
conductor. The direction of the force felt by the conductor is found by
applying Fleming’s left hand rule.
Generated force is maximum in the case of when the direction of
current is at right angles to the direction of the magnetic field.
Devices that use current-carrying conductors and magnetic fields
include electric motor, electric generator, loudspeakers, microphones and
measuring instruments.
Q. Explain Fleming's left hand rule.
Ans. According to Fleming's left hand rule, stretch the thumb, forefinger
and middle finger of your left hand such that they are mutually
perpendicular. If the fore finger points in the direction of magnetic field and
the middle finger in the direction of current, then the thumb will point in the
direction of motion or the force acting on the conductor.
Q. An electron enters a magnetic field at right angles to it, as shown in Fig.
The direction of force acting on the electron will be
Ans. As the direction of current is opposite of the
direction of electrons, so by applying Fleming's left
hand rule:-
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We get the direction of force acting on the electron will be downward.
Q. Which of the following properties of a proton can change while it moves
freely in a magnetic field?
Ans. Moving of protons means motion of electrons which means flow of
electricity. When electricity flows in a magnetic field, it experiences a force
which changes its velocity and as the velocity changes its momentum will
also change(momentum = mass x volume). So the correct options are (c)
and (d).
Q. What are the factors on which displacement of a current carrying
conductor in a magnetic field depends?
Ans. The magnitude of the displacement depends on :-
1. Magnitude of the current directly depends on the displacement.
2. Magnitude of the magnetic field directly depends on the
displacement.
3. Distance of the conductor inversely depends on the displacement.
4. Length of the conductor directly depends on the displacement.
The direction of the displacement depends on :-
1. The direction of current.
2. The direction of the magnetic field.
Q. A positively-charged particle (alpha-particle) projected towards west is
deflected towards north by a magnetic field. The direction of magnetic field
is
Ans. The direction of positively-charged particle towards west so the
direction of current is also towards west and because the deflection is
towards north so by applying Fleming's left hand rule:-
We get the direction of the magnetic field in the upward
direction.
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Q. Explain the mechanism of domestic electric circuits.
Ans. A domestic electric circuit works by supplying electricity from power
sources to appliances through a network of wires, switches, and other
components:
Power supply:- Electricity comes from power generation plants and is
delivered to homes through overhead power poles or underground cables
also known as Mains.
Wires:- The power supply consists of three types of wires:
1. Live wire : Usually red, this wire carries electricity to appliances and
is +ve terminal.
2. Neutral wire : Usually black, this wire carries electricity to appliances
and is -ve terminal.
3. Earth wire : Usually green, this wire runs through the circuit and is
used as a safety measure.
Fuses and switches:- A fuse protects the circuit and appliances by
stopping the flow of high current. A switch controls the on-off mechanism of
the circuit.
Appliances:- Appliances are connected in parallel, so that turning one on
or off doesn't affect the others.
Electric meter:- An electric meter records the amount of electricity
consumed by the household.
Circuit types:- There are two types of circuits in a household: 5 A for lower
power appliances and 15 A for higher power appliances.
Figure of a domestic circuit is :-
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Q. Difference between Alternating Current and Direct Current.
Ans.
Alternating Current(AC)
Direct Current(DC)
Direction of the flow of electricity
changes every 0.01 s.
Direction of the flow of electricity
does not change.
In the case of AC, electric power
can be transmitted over long
distances without much loss of
energy.
In the case of DC, electric power
cannot be transmitted over long
distances without much loss of
energy.
Frequency of AC is nonzero, in
India it is 50Hz.
Frequency of DC is zero.
Sources of AC are :- Power plant,
AC generators etc.
Sources of DC are :- Battery, DC
generators etc.
Q. How does earth wire work?
Ans. The earth wire, which has insulation of green colour, is usually
connected to a metal plate deep in the earth near the house. This is used
as a safety measure, especially for those appliances that have a metallic
body, for example, electric press, toaster, table fan, refrigerator, etc. The
metallic body is connected to the earth wire, which provides a
low-resistance conducting path for the current. Thus, it ensures that any
leakage of current to the metallic body of the appliance keeps its potential
to that of the earth, and the user may not get a severe electric shock.
Q. What does overloading mean?
Ans. When the flow of current in a circuit exceeds its limit then the situation
is known as overloading. It occurs because of the following reasons:-
1. When too many high-power appliances are turned on at the same
time.
2. Connecting too many appliances to one socket.
3. Accidental hike in the supply voltage.
Q. What happens during overloading?
Ans. During overloading the flow of current in the circuit exceeds its limit so
the wire overheats and may melt, which increases the risk of fire.
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Q. What does short-circuiting mean?
Ans. The situation when the live wire and the neutral wire come into direct
contact, is called short-circuiting. In such a situation, the current in the
circuit abruptly increases because the resistance of the circuit becomes
almost zero.
Q. What are the consequences of short-circuiting?
Ans. Short-circuiting can cause sparks, overheating of wires, and
potentially damage appliances or even start a fire.
Q. How to provide safety against overloading and short-circuiting?
Ans. The use of an electric fuse prevents the electric circuit and the
appliance from the consequences of short-circuiting by stopping the flow of
unduly high electric current. The Joule heating that takes place in the fuse
melts it to break the electric circuit.
Q. Name two safety measures commonly used in electric circuits and
appliances.
Ans. Switch and earth wire are the two safety devices.
Q. 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.
Ans. Circuit :- Electric oven:-
V = 220 V P = 2KW
= 2000 W
I = 5 A
Drawn current from the circuit by the oven =
𝑃
𝑉
=
2000
220
=
9 . 09 𝐴
Because the current limit of the circuit is 5 A and the drawn current is 9.09A
hence this is the case of overloading.
Q. What precaution should be taken to avoid the overloading of domestic
electric circuits?
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Ans. Precaution should be taken to avoid overloading are :-
1. Avoid using too many appliances at once.
2. Ensure that the appliances we use are within the circuit's safe limit.
3. Shouldn't connect too many appliances to one socket.
4. Use of an electric fuse in series to protect the circuit.
5. Ensuring that all electrical circuits are properly earthed
Exercises
Q. Which of the following correctly describes the magnetic field near a long
straight wire?
Ans. (d) The field consists of concentric circles centred on the wire.
Q. At the time of short circuit, the current in the circuit
Ans. (c) increases heavily.
Q. State whether the following statements are true or false.
(a) The field at the centre of a long circular coil carrying current will be
parallel straight lines.
Ans. True
(b) A wire with a green insulation is usually the live wire of an electric
supply.
Ans False
Q. List two methods of producing magnetic fields.
Ans. The two methods are :-
1. Magnetic fields can be produced by passing electric current through a
conductor.
2. Magnetic fields can be produced by any permanent magnet.
Q. When is the force experienced by a current–carrying conductor placed
in a magnetic field largest?
Ans. The force is maximum in the case of when the direction of current is
at right angles to the direction of the magnetic field.
Q. Imagine that you are sitting in a chamber with your back to one wall. An
electron beam, moving horizontally from the back wall towards the front
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wall, is deflected by a strong magnetic field to your right side. What is the
direction of the magnetic field?
Ans.
Since the direction of the current is opposite to the direction of electrons,
the current is coming from the front of the wall. By applying Flemin’s left
hand rule we get the direction of the magnetic field is toward downward.
Q. State the rule to determine the direction of a
(i) magnetic field produced around a straight conductor-carrying current.
Ans. Maxwell’s Right hand thumb rule.
(ii) force experienced by a current-carrying straight conductor placed in a
magnetic field which is perpendicular to it.
Ans. Fleming’s Left hand rule.
(iii) current induced in a coil due to its rotation in a magnetic field.
Ans. Fleming’s Right hand rule.
Q. When does an electric short circuit occur?
Ans. When the live wire and the neutral wire come into direct contact then
an electric short circuit occurs.
Q. What is the function of an earth wire? Why is it necessary to earth
metallic appliances?
Ans. The metallic body is connected to the earth wire, which provides a
low-resistance conducting path for the current. Thus, it ensures that any
leakage of current to the metallic body of the appliance keeps its potential
to that of the earth, and the user may not get a severe electric shock.
If the earth wire is not connected to the metallic appliances then in
the case of leakage of the current, users get a severe electric shock so to
prevent this it is necessary to earth metallic appliances.
