# CBSE Solutions for Class 10 English

#### GSEB std 10 science solution for Gujarati check Subject Chapters Wise::

Name two safety measures commonly used in electric circuits and appliances. [2010,2012,2014]

જવાબ : (a) Earthing
(b) Electric fuse

What is the principle of an electric motor? 

જવાબ : An electric motor works on the principle that when a current-carrying coil is placed in a magnetic field, it experiences a torque which tends to rotate it.

Why does a compass needle get deflected when brought near a bar magnet?

જવાબ : This is because of magnetic field of the bar magnet.

Consider a circular loop of wire lying in the plane of the table. Let the current passes through the loop clockwise. Apply the right- hand rule to find out the direction of the magnetic field inside and outside the loop.

જવાબ : (a) Direction of magnetic field inside the loop is perpendicular to the plane of the paper inward (anticlockwise).
(b) Direction of magnetic field outside the loop is perpendicular to the plane of the paper outward (clockwise).

Why do not two magnetic lines of forces intersect each other? [2011,2012,2015]

જવાબ : If the magnetic lines of forces intersect, there will be two different directions of magnetic field at that point, which is not possible.

When is the force experienced by a current-carrying conductor placed in a magnetic field largest?

જવાબ : When the length of current-carrying conductor and direction of magnetic field are perpendicular to each other, the maximum force is experienced by the current-carrying conductor.

Name any two appliances which are based on the application of heating effect of electric current.

જવાબ : Room heater and geyser.

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.

જવાબ : Yes, when a current in coil A changes, magnetic field lines linked with coil B also change. Hence, due to change in number of magnetic field lines, there is an induced current in coil B.

The magnetic field associated with a current-carrying straight conductor is in anticlockwise direction. If the conductor was held along the east-west direction, what will be the direction of current through it? Name and state the rule applied to determine the direction of current.

જવાબ : Direction of current – east to west as determined by Right-hand thumb rule. Ri’-lu-Uand Thumb Rule: If we hold a current-carrying conductor by right hand in such a way that the stretched thumb is along the direction of current, then the curly fingers around the conductor represents the direction of field lines of magnetic field.

Insulation cover of which colour is conventionally used for earth wire? Why is an earth wire connected to metallic parts of appliances?

જવાબ : For earth wire, green or yellow colour insulation is used. The earth wire provides the low resistance conducting path for the current and maintains the potential of appliances body with that of the earth. So, earth wire is used as a safety measure.

Why does a compass needle gets deflected when brought near a bar magnet?

જવાબ : A compass needle is, in fact, a small bar magnet. If this is brought near another bar magnet, the like poles repel and the needle gets deflected.
40. Name the type of current:
(a) used in household supply. (b) given by a cell.
(a) Alternating current. (b) Direct current.

Name the physical quantities which are indicated by the direction of thumb and forefinger in the Fleming’s right hand rule?

જવાબ : In Fleming’s right hand rule,
thumb indicates — direction of motion of the conductor; forefinger indicates — direction of magnetic field.

Give one application of electromagnetic induction.

જવાબ : This phenomenon is used in electric generator.

State the direction of magnetic field in the following case: જવાબ : Perpendicular to the plane of paper in the outward direction by using Fleming’s left hand rule.

Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B ? Give reason.

જવાબ : Yes, some current will be induced in the coil B. When the current in coil A is changed, some current is induced in the coil B. Due to change in current in coil A, the magnetic field lines linked with coil A and with coil B get changed. This sets up induced current in coil B.

Name some devices in which electric motors are used.

જવાબ : Electric motor is used in the appliances like electric fans, washing machine, mixers, grinders, blenders, computers, MP3 players, etc.

When is the force experienced by a current-carrying conductor placed in a magnetic field largest ?

જવાબ : When the conductor carries current in a direction perpendicular to the direction of the magnetic field, the force experienced by the conductor is largest.

List three sources of magnetic fields.

જવાબ : (i) Current carrying conductor
(ii) Electromagnets
(iii) Permanent magnets

Name two safety measures commonly used in electric circuits and appliances.

જવાબ : (i) Earthing and
(ii) Electric fuse.

Which sources produce alternating current ?

જવાબ : Alternating current is produced by AC generators of nuclear power plants, thermal power plants, hydroelectric power stations, etc.

Name some sources of direct current.

જવાબ : Some of the sources of direct current are dry cells, button cells, lead accumulators.

Explain different ways to induce current in a coil.

જવાબ : Different ways to induce current in a coil are :
1.    moving a magnet towards or away from the coil or vice-versa, and
2.    changing current in the neighbouring coil.

What is the role of the split ring in an electric motor ?

જવાબ : The split ring reverses the direction of current in the armature coil after every half rotation, i.e., it acts as a commutator. The reversed current reverses the direction of the forces acting on the two arms of the armature after every half rotation. This allows the armature coil to rotate continuously in the same direction.

Why don’t two magnetic lines of force intersect each other ?

જવાબ : This is due to the fact that the resultant force on a north pole at any point can be only in one direction. But if the two magnetic field lines intersect one another, then the resultant force on north pole placed at the point of intersection will be along two directions, which is not possible.

List the properties of magnetic lines of force.

જવાબ : Properties of magnetic lines of force :
•    The magnetic field lines originate from the north pole of a magnet and end at its south pole.
•    The magnetic field lines become closer to each other near the poles of a magnet but they are widely separated at other places.
•    Two magnetic field lines do not intersect one another.

Why does a compass needle get deflected when brought near a bar magnet ?

જવાબ : The magnetic field of the magnet exerts force on both the poles of the compass needle. The forces experienced by the two poles are equal and opposite. These two forces form a couple which deflects the compass needle.

What is the function of an earth wire? Why is it necessary to earth metallic appliances?

જવાબ : The metallic body of electric appliances is earthed by means of earth wire. Any leakage of electric wire is transferred to the ground by means of earth wire. This prevents the user of the electric appliance from getting electric shocks. This is the reason why it is important for the metallic appliances to be earthed.

Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.

જવાબ : When the current in coil A changes, the magnetic field associated with it also changes. As a result the magnetic field around coil B undergoes change. The change in the magnetic field of coil B induces current in it.

Name some devices in which electric motors are used.

જવાબ : A few devices in which electric motors are used are:
•    Electric fans
•    Water pumps
•    Mixers
•    Washing machines

When is the force experienced by a current–carrying conductor placed in a magnetic field largest?

જવાબ : When the direction of the current is perpendicular to the direction of the magnetic field is when the force experienced is the largest.

What precaution should be taken to avoid the overloading of domestic electric circuits?

જવાબ : A few of the precautions to be taken to avoid the overloading of domestic electric circuits are as follows:
•    Connecting too many devices to a single socket should be avoided
•    Using too many appliances at the same time should be avoided
•    Faulty appliances should not be connected to the circuit

Choose the correct option.
A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each
1.    two revolutions
2.    one revolution
3.    half revolution
4.    one-fourth revolution

જવાબ : c. half revolution
When a rectangular coil is rotated in magnetic field, the direction of the induced current changes once in half revolution. As a result, the direction of the current in the coil remains the same.

Which sources produce alternating current?

જવાબ : Power plants and AC generators are some of the sources that produce alternating current.

Name some sources of direct current.

જવાબ : DC generator and cell are some sources of direct current.

State the principle of an electric generator.

જવાબ : Electric generator works on the principle of electromagnetic induction. In a generator, electricity is generated by rotating a coil in the magnetic field.

Explain different ways to induce current in a coil.

જવાબ : Following are the different ways to induce current in a coil:
•    If the coil is moved rapidly between the two poles of horse shoe magnet, electric current is induced in the coil.
•    When a magnet is moved relative to the coil, an electric current is induced in the coil.

What is the role of split ring in an electric motor?

જવાબ : Split ring plays the role of commutator in an electric motor. The commutator reverses the direction of the current flowing through the coil after each half rotation of the coil. Due to this reversal of current, the coil continues to rotate in the same direction.

What is the principle of an electric motor?

જવાબ : The working principle of electric motor is based on the magnetic effect of current. A current carrying conductor when placed in a magnetic field experiences force and rotates. The direction of the rotation of the conductor can be determined by Fleming’s Left hand rule.

State Fleming’s left-hand rule.

જવાબ : Fleming’s Left hand rule states that if we arrange our thumb, forefinger and middle finger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the forefinger points towards the direction of magnetic field and the middle finger points towards the direction of current.

In Activity 13.7, how do we think the displacement of rod AB will be affected if (i) current in rod AB is increased; (ii) a stronger horse-shoe magnet is used; and (iii) length of the rod AB is increased?

જવાબ : A current carrying conductor when placed in a magnetic field experiences force. The magnitude of this force will increase with the increase in the amount of current, length of conductor and the strength of the magnetic field. Hence, the strength of the magnetic force exerted on the rod AB and its displacement will increase if
1.    The current in rod AB is increased
2.    Stronger horse shoe magnet is used
3.    When the length of the rod AB increases

Why don’t two magnetic field lines intersect each other?

જવાબ : If two magnetic field lines intersect then at the point of intersection the compass needle shows two different directions, which is not possible, hence they do not intersect with each other.

By convention the magnetic field lines emerge from …………… pole and merge at …………… pole.

A coil of many circular turns of insulated copper wire wrapped closely in shape of a cylinder is called a ……………

જવાબ : solenoid

An electric motor is rotating device that converts …………… energy to …………… energy.

જવાબ : electrical, mechanical

AC generator converts …………… energy into …………… energy.

જવાબ : mechanical, electrical

The difference between the direct current and alternating current is that the direct current flows in …………… direction, whereas the alternating current …………… its direction periodically.

જવાબ : one, reverses

At the centre of current carrying loop the magnetic field appears to be a ……………

જવાબ : straight line

Why does a compass needle get deflected when brought near a bar magnet?

જવાબ : The compass needle is a small magnet. When the compass needle is brought close to a bar magnet, the magnetic field lines of the compass needle interact with the magnetic field lines of bar magnet, which causes the compass needle to deflect.

List the properties of magnetic field lines.

જવાબ : The properties of magnetic field lines are as follows:
•    Magnetic field lines do not intersect with each other.
•    They emerge from the North Pole and terminate at the South Pole.
•    Inside the magnet, the direction of the field lines is from the South Pole to the North Pole.

State Fleming’s left hand rule with a labelled diagram. (CBSE 2005, 2010, 2011, 2012)

જવાબ : Fleming’s left hand rule
Statement : Stretch the left hand such that the thumb, first finger and the central finger are mutually perpendicular to each other. If the First finger points in the direction of the magnetic Field and the Central finger points in the direction of Current, then the thumb will point in the direction of Motion (or Force) as shown in figure 24. Thus, in Fleming’s left hand rule, first finger shows the direction of the magnetic field. The central finger shows the direction of electric current flowing in the conductor. Thumb shows the direction of force on the conductor or the direction of motion of the conductor.

List the properties of magnetic field lines. (CBSE 2015)
Or
Write four properties of magnetic field lines. (CBSE (Delhi) 2010, 2011, 2012, 2013)

જવાબ :

1. Magnetic field lines are closed continuous curves.
2. The tangent at any point on the magnetic field line gives the direction of the magnetic field at that point.
3. No two magnetic field lines can cross each other.
4. Magnetic field lines are crowded in a region of strong magnetic field and magnetic field lines diverge in a region of weak magnetic field.

Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring an electric motor?

જવાબ : An electric motor is a device which converts electrical energy into mechanical energy.
Construction: It consists of a rectangular coil called armature curved magnet pieces, commutator and carbon brushes.
Principle: It works on the principle that when a current-carrying coil is placed normally in a magnetic field, it experiences a torque which tends to rotate it. Working:

1. When a current flows through the coil, arms AB and CD experience a force. According to Fleming’s left hand rule, arm AB of the coil experiences a force in the downward direction. Similarly, arm CD of the coil experiences a force in the upward direction. Two equal and opposite forces constitute a couple and hence the coil will rotate in anticlockwise direction.
2. When the coil reaches the vertical position, no current flows in the coil and no force actstm the coil in this position.
3. Now coil rotates further and side AB is moved on the right, with its commutator segment touching the right hand brush so it has downward force acting it. Similarly, side CD has an upward force on it. Thus, the couple always acts in the same direction (clockwise) and the coil spins.

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. [2012, 2013]

જવાબ : When a solenoid carrying current is freely suspended, it comes to rest along a particular direction because it behaves like a bar magnet with fixed polarities at its ends.

Yes, the north and south poles of current-carrying solenoid can be determined with the help of a bar magnet

On bringing south pole of a bar magnet near one of the ends of solenoid, if the end moves towards the south pole of the bar magnet, it is north pole. But if the end moves away from the south pole of the bar magnet, it is south pole.

What is the function of an earth wire? Why is it necessary to earth metallic appliances?

જવાબ : To avoid electric shocks, the metal body of an electrical device is ‘earthed’. A wire called ‘earth wire’ is used to connect the metal body of the electrical device to the earth, which is at zero potential. In household circuits, we have three wires, the live wire, the neutral wire and the earth wire. One end of the earth wire is connected to the device and the other end of the wire is connected to the earth. We now say that the device is “earthed” or “grounded”. Usually the three wires are connected to a three-pin plug. The neutral wire or the earth connection carries the high current to the earth from the device and prevents an electric shock.

What is the function of an earth wire ? Why is it necessary to earth metallic appliances ?

જવાબ : Earth wire is a safety measure that provides a low resistance conducting path to the current. Sometimes due to excess heat or wear and tear, the live wire comes in direct contact with the metallic cover of the appliances, which can give an electric shock on touching them. To prevent from the shock the metallic part is connected to the earth through a three-pin plug due to which the current flows to the earth at the instant there is a short circuit.

It is necessary to earth metallic appliances because it ensures that if there is any current leakage in the metallic cover, the potential of the appliance becomes equal to that of the earth. The potential of the earth is zero. As a result, the person handling the appliance will not get an electric shock.

State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current (it) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (in) current induced in a coil due to its rotation in a magnetic field.

જવાબ : (i) Right hand thumb rule : If the current carrying conductor is held in the right hand such that the thumb points in the direction of the current, then the direction of the curl of the fingers will give the direction of the magnetic field.
(ii) Fleming’s left hand rule : NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current Stretch the forefinger, the central finger and the thumb of the left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field, the middle finger in the direction of current, then the thumb points in the direction of force in the conductor.
(iii) Fleming’s right hand rule : Stretch the thumb, forefinger and the central finger of the right hand mutually perpendicular to each other. If the forefinger points in the direction of magnetic field, thumb in the direction of motion of the conductor, then the middle finger points in the direction of current induced in the conductor.

Imagine that you are sitting in a 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 ?

જવાબ : Here the electron beam is moving from our back wall to the front wall, so the direction of current will be in the opposite direction, from front wall towards back wall or towards us. The direction of deflection (or force) is towards our right side.
We now know two things :

• direction of current is from front towards us, and
• direction of force is towards our right side.
Let us now hold the forefinger, middle finger and thumb of our left hand at right angles to one another. We now adjust the hand in such a way that our centre finger points towards us (in the direction of current) and thumb points towards right side (in the direction of force). Now, if we look at our forefinger, it will be pointing vertically downwards. Since the direction of forefinger gives the direction of magnetic field, therefore, the magnetic field is in the vertically downward direction.

How docs 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.

જવાબ : A solenoid behaves like a magnet in the following ways.

• The magnetic field produced by a current carrying solenoid is very much similar to that of a bar magnet.
• Like a bar magnet, one end of the solenoid has N-polarity while the other end has S-polarity.
To determine the north and south poles, we bring N-pole of the bar magnet near one end of the solenoid. If there is an attraction, then that end of the solenoid has south polarity and the other has north polarity. If there is a repulsion, then that end of the solenoid has north polarity and the other end has south polarity because similar poles repel each other.

State the principle of an electric generator.

જવાબ : The electric generator works on the principle that when a straight conductor is moved in a magnetic field, then current is induced in the conductor.
In an electric generator, a rectangular coil is made to rotate rapidly in the magnetic field between the poles of a horse-shoe type magnet. When the coil rotates, it cuts the magnetic field lines due to which a current is produced in the coil.

Consider a circular loop of wire lying on 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.

જવાબ : As shown in figure alongside, each section of wire produces its concentric set of lines of force. By applying right hand thumb rule, we find that all the sections produce magnetic field downwards at all points inside the loop while at the outside points, the field is directed upwards. Therefore, the magnetic field acts normally into the plane of the paper at the points inside the loop and normally out of the plane of paper at points outside the loop. The magnetic field in a given region is uniform. Draw a diagram to represent it. [CBSE 2013, 2014]

જવાબ : A uniform magnetic field in a region is represented by drawing parallel straight lines, ail pointing in the same direction.
For example, the uniform magnetic field which exists inside a current-carrying solenoid can be represented by parallel straight lines pointing from its S-pole to N-pole (as shown in figure). State Fleming’s left hand rule. [CBSE 2018]

જવાબ : Fleming’s left hand rule : Stretch the first finger, the middle finger and the thumb of your left hand mutually perpendicular to each other in such a way that the first finger represents the direction of the magnetic field, the middle finger represents the direction of the current in the conductor, then the thumb will represent the direction of motion of the conductor. When does an electric short circuit occur?

જવાબ : Listed below are two instances of when a short-circuit can occur:

1) When too many appliances are connected to a single socket or when high power rating appliances are connected to a light circuit, the resistance of the circuit becomes low as a result the current flowing through the circuit becomes very high. This condition results in a short-circuit.

2) When live wires whose insulation have worn off come in contact with each other, the current flowing in the circuit increases abruptly which results in a short circuit.

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?

જવાબ : (i) When a bar magnet is pushed into the coil, current is induced in the coil momentarily as a result the galvanometer deflects in a particular direction momentarily.

(ii) When the bar magnet is withdrawn from inside the coil, current is induced momentarily but in the opposite direction and the galvanometer deflects in the opposite direction momentarily.

(iii) When the bar magnet is held stationary inside the coil, no current will be induced as a result there will be no deflection in the galvanometer.

Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?

જવાબ : An electric motor is a device that converts electrical energy to mechanical energy. It works on the principle of magnetic effect of current. The figure listed below shows a simple electric motor. When current is made to flow through the coil MNST by closing the switch, the coil starts to rotate in the anticlockwise direction. This is due to the downward force acting on the length MN and simultaneously an upward force acting along the length ST. As a result of which the coil rotates in the anticlockwise direction. Current in the length MN flows from M to N and the magnetic fields act from left to right normal to the length MN. According to Fleming’s Left Hand rule, a downward force acts along the length MN. Similarly, the current along the length ST flows from S to T and the magnetic field acts from left to right. Therefore, an upward force acts along the length ST. These two forces together cause the coil to rotate anti-clockwise. After half a rotation, the position of MN and ST interchange. The half ring C come in contact with brush B and the half ring D comes in contact with rush C. Hence the direction of current in the coil MNST gets reversed.

Imagine that you are sitting in a 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?

જવાબ : The direction of the magnetic field can be determined using the Fleming’s Left hand rule. The direction of the magnetic field will be perpendicular to the direction of current and the direction of deflection, i.e., either upward or downward. The direction of the current is from the front wall to the back wall because negatively charged electrons move from the back wall to the front wall. The directed of the magnetic force is rightward. Hence, using Fleming’s left hand rule it can be concluded that the direction of the magnetic field inside the chamber is downward.

List two methods of producing magnetic fields.

જવાબ : Following are the methods of producing magnetic fields:

• By using a permanent magnet we can produce magnetic field and it can be visualized by spreading iron fillings on a white paper and keeping a magnet beneath the paper.
• A current carrying straight conductor produces magnetic field.
• Different types of conductors such as solenoid and circular loop can be used to see the presence of magnetic field.

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.

જવાબ : The current drawn by the electric oven can be calculated using the formula

P = V × I

I = P/V

Substituting the values, we get

I = 2000 W/220 V = 9.09 A

The current drawn by the electric oven is 9.09 A which exceeds the safe limit of the circuit. This causes the fuse to melt and break the circuit.

Name two safety measures commonly used in electric circuits and appliances.

જવાબ : The safety measured commonly used in electric circuits are as follows:

1. Fuse
Each circuit should be connected to a fuse because a fuse prevents the flow of excessive current through the circuit. When the current in the circuit exceeds the maximum limit of the fuse element, the fuse melts to stop the flow of current protecting the appliance connected to circuit.

1. Earthing
Earthing protects the user from electric shocks. Any leakage of current in an appliance is transferred to the ground by earthing and the people using the appliance is prevented from getting electrocuted.

A positively-charged particle (alpha-particle) projected towards the west is deflected towards north by a magnetic field. The direction of magnetic field is

• towards south
• towards east
• downward
• upward

જવાબ : The direction of the magnetic field can be determined using the Fleming’s Left hand rule. According to the rule, if we arrange our thumb, forefinger and the middle finger of the left hand right perpendicular to each other, then the thumb points towards the direction of the magnetic force, the middle finger the direction of current and the forefinger the direction of magnetic field. Since the direction of positively charged particle is towards west, the direction of the current will also be towards the west. The direction of the magnetic force is towards the north, hence the direction of magnetic field will be upward according to Fleming’s Left hand rule.

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Match the following columns

 Column I Column II 1. Right hand thumb rule (а) converts electrical energy into mechanical energy 2. Fleming’s left hand rule (b) gives the direction of magnetic field around a conductor 3. Fleming’s right hand rule (c) converts mechanical energy into electrical energy 4. Alternating current (d) gives the direction of force on current carrying conductor placed in magnetic field 5. Direct current (e) the direction of current changes periodically 6. Electric motor (f) gives the direction of induced current 7. Generator (g) current always flows in one direction.

જવાબ :

 Column I Column II 1. Right hand thumb rule (b) gives the direction of magnetic field around a conductor 2. Fleming’s left hand rule (d) gives the direction of force on current carrying conductor placed in magnetic field 3. Fleming’s right hand rule (f) gives the direction of induced current 4. Alternating current (e) the direction of current changes periodically 5. Direct current (g) current always flows in one direction. 6. Electric motor (а) converts electrical energy into mechanical energy 7. Generator (c) converts mechanical energy into electrical energy

 a. Principle of electric generator Fuse b. Magnetic field around a straight conductor Electromagnetic induction c. The safety device which is used to protect the circuit from short circuiting and overloading Concentric circles

જવાબ :

a. Electromagnetic induction
b. Concentric circles
c. Fuse

 a. The direction of magnetic field produced by a current carrying conductor can be found out by using Red b. The current which reverses its direction periodically Right hand thumb rule c. The device which convert electrical energy into mechanical energy Alternating current d. Colour of insulation of live wire Electric motor

જવાબ :

a. Right hand thumb rule
b. Alternating current
c. Electric motor
d. Red