Magnetic Effect of Current : Complete Set of Questions



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This set of questions contains all the possible concepts
which could be asked in the examination

MAGNET 

Q.1  How two magnets apply force on each other?  (2 Marks)

Like poles of a magnet repel each other and unlike poles attract each other


Q.2  Name the two poles of a magnet? (2 Marks)

North Pole and south pole.


Q.3  What is meant by the term ‘magnetic field’? (2 Marks)

The space surrounding a magnet in which magnetic force can be experienced is called magnetic field. It has both magnitude as well as direction.


Q.4  Define magnetic field lines? (2 Marks)

To describe magnetic field, we draw magnetic field lines. Magnetic field lines are the lines drawn in a magnetic field region along which the north pole of a magnet points.


Q.5  Give three properties of the magnetic field lines? (3 Marks)

Properties of Magnetic Field Lines

1. Magnetic field lines originate from North Pole and end at South Pole.

2. Magnetic field lines come closer to one another near the poles of magnet but widely separated at other places.

3. Magnetic field lines do not intersect each other.


Q.6 Explain why, two magnetic field lines do not interest each other? (2 Marks)

Magnetic field lines never intersect each other because resultant force on North Pole can only be in one direction. Had the lines intersected, it would be in two directions which is not possible.


Q.7 State the direction of the magnetic field inside the bar magnet? (1 Mark)

The direction of magnetic field inside the bar magnet is from south to north.


Q.8 In a pattern of magnetic field lines due to a bar magnet, how can the regions of relative strength be identified? (2 Marks)

The region having high density of field lines has high density of magnetic field. But the regions where magnetic field lines have low density have lower value of magnetic field.


Q.9 You are given the magnetic field pattern of a magnet. How will you find out from it where the magnetic field is strongest? (2 Marks)

The region having high density of field lines has high density of magnetic field. But the regions where magnetic field lines have low density have lower value of magnetic field.


Q.10 Name an instrument in which the directive property of a magnet is used?(1 Mark)

Magnetic compass

 

Magnetic field due to Current carrying wires

Q.11 State the observation made by Oersted on the basis of his experiment with current carrying conductor?    (2 marks) 

Oersted observed that a current carrying conductor can deflect a magnetic compass placed nearby. On the basis of this observation, he concluded that a current carrying creates magnetic field.


Q.12 What happens to the deflection of needle of magnetic compass  when current in the conductor is increased? (1 Mark)

The deflection increases.


Q.13 State the form of magnetic field lines around a straight current carrying conductor. (1 Mark)

Concentric circular rings


Q.14 State qualitatively the effect of inserting an iron core into a current carrying solenoid. (1 Mark)

When a soft iron core is inserted in a current carrying solenoid, magnetic field due to the solenoid increases.


Q.15 Name the rule for finding the direction of magnetic field produced by a straight current carrying conductor. (1 Mark)

Right Hand Thumb Rule


Q.16 State and explain Maxwell’s right – hand thumb rule. (2 Marks)

Maxwell's Right hand thumb rule states that if we hold the current carrying wire in the right hand and if the thumb points towards the current, the direction in which the fingers encircle gives the direction of Magnetic field.


Q.17 Name the scientist who discovered the magnetic effect of current. (1 Mark)

Hans Christian Orsted


Q.18 Define a solenoid.Compare the magnetic field produced by a solenoid with that of a bar magnet? (2 Marks)

Solenoid is a long coil containing a large number of close turns of insulated copper wire. The Magnetic field lines of a Bar Magnet are similar to that of solenoid.


Q.19 What type of “core” should be put inside a current – carrying solenoid to make an electromagnet? (1 Mark)

A soft iron core


Q.20 What is an electromagnet? How does it differ from a permanent magnet? State three factors on which the strength of an electromagnet depends? (5 Marks)

Electromagnet is a magnet formed by putting a soft iron core inside a current carrying solenoid. It is a temporary magnet as the magnetic effect is lost when there is no current flowing into it. The strength of magnetic field of electromagnet depends on the value of current, number of turns and the nature of core inserted in it.


Q.21 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. (5 Marks)

Solenoid behaves like a magnet in the way that if current is passed through it, it produces magnetic field similar to a bar magnet.

To determine the poles of a magnet, we can use a bar magnet. Say we bring the north pole of the bar magnet near a pole of the solenoid. If the pole is repelled, it must be North pole. If it is attracted, it must be the south pole. Once one pole is determined, other pole will be the other one.


Q.22  What is Maxwell’s corkscrew rule? For what purpose is it used? (3 Marks)

Maxwell's corkscrew is used to find direction of magnetic field due to a straight current carrying wire. According to it, we need to imagine a screw being tightened. The direction of current is compared with the direction in which the screw moves. The sense of rotation of the screw gives the direction of magnetic field.


Q.23 What are the various ways in which the strength of magnetic field produced by a current- carrying circular coil can be increased? (2 Marks)

The strength of magnetic field by a current carrying wire can be increased by increasing current, by increasing no. of loops in the coil and the size of the coil.


Q.24 What are the differences between a Bar Magnet(or Permanent Magnet) and electromagnet? (2 Marks)


Q.25 List the three ways in which the magnet field strength of current carrying solenoid can be increased? (3 Marks)

The three ways in which the magnetic field strength of a current carrying solenoid can be increased are :

1. Increasing current in the solenoid

2. Increasing number of turns in the solenoid

3. Inserting a soft iron core in the solenoid


Q.26  Explain why, an electromagnet is called a temporary magnet? (1 Mark)

Electromagnet is called a temporary magnet because once the current is switched off, the magnetic field exists no more.


Q.27  Explain why, the core of an electromagnet should be of soft iron and not of steel? (2 Marks)

If we use steel as the core of an electromagnet, the magnetic field of the electromagnet will be much lesser compared to soft iron. Also, in case of steel, the magnetic effect of the solenoid will remain even after the current is switched off which is not a desired property for an electromagnet.


Q.28  Distinguish between a solenoid and a bar magnet. Draw the magnetic lines for both. (5 Marks)

Magnetic Force on current carrying wire

Q.29  Define electromotive force. (2 Marks)

When a current carrying wire is placed in a magnetic field, the force experienced by the wire is called the electromotive force.


Q.30  If the current in a wire is flowing in the vertically downward direction and a magnetic field is applied from west to east, what is the direction of force on the wire? (1 Mark)

North to south


Q.31  What happens when a current- carrying conductor is placed in a magnetic field? (1 Mark)

When a current carrying conductor is placed in the magnetic field, it experiences a magnetic force.


Q.32  In a statement of Fleming’s left-hand rule, what do the following represent? (3 Marks)

(a)  Direction of centre finger.

(b)  Direction of forefinger.

(c)  Direction of thumb.

(a) Direction of current

(b) Direction of magnetic field

(c) Direction of motion


Q.33 Explain why, a freely suspended magnet always points in the north-south direction? (2 Marks)

Earth acts as a magnet.  Due to this a weak magnetic field exists on the surface of earth in north-south direction. This magnetic field applies force on the freely suspended magnet in north-south direction. So a freely suspended magnet always points in the north-south direction.

Q.34  For what angle between magnetic field and wire, the force is maximum? (1 Mark)

90 degrees


Q.35 Magnetic field is from east to west. A wire carries current from north to south. Find the direction of force. Describe. (3 Marks)

We should use Fleming's left hand rule to find the direction on force. The force finger should be pointed in direction of magnetic field (east to west). The center finger should point in the direction of current (north to south).  Thumb will point in downward direction, so the force on wire will act downwards.


Q.36 An electron moves from north to south in a magnetic field from east to west. In which direction will the force on electron be? (1 Mark)

Upwards.

 

Motor

Q.37  Name one device which works on the magnetic effect of current. (1 Mark)

Electric Motor


Q.38  What is electric motor? With help of a diagram, describe the working of an electric motor. (5 Marks)

Electric Motor is a device that converts electrical energy into mechanical energy.

The working of an electric motor can be described in following steps.

1. Due to battery, current flows in the loop placed in magnetic field.

2. Magnetic field applies force on loop so that it rotates. Thus, electrical energy is converted into mechanical energy.

3. But for loop to rotate continuously in one direction, direction of force on wires should keep changing after every half revolution.

4. This is achieved by split rings. They facilitate the change in direction of current.

5. Reversal of direction of current reverses the direction of forces acting on the coil. The change in direction of force pushes the coil; and it moves another half turn.

6. Thus the loop keeps rotating.


Q.39  Name the device which is used to reverse the direction of current in the coil of a motor. (1 Mark)

Commutator


Q.40  A motor converts one form of energy into another. Name the two forms. (2 Marks)

A motor converts electrical energy to mechanical energy


Q.41  Name the device which converts electrical energy into mechanical energy? (1 Mark)

Electrical motor


Q.42  What is other name of the split ring used in an electric motor? (1 Mark)

Commutator


Q.43  What is the function of commutator in an electric motor? (1 Mark)

Commutator is a device which reverses the direction of flow of electric current through a circuit.


Q.44  What is the principle of electric motor? (1 Mark)

When a current carrying wire is moved in a magnetic field, it experiences a magnetic force.


Q.45  Describe the construction of a motor. (5 Marks)

The construction of a motor can be described in following points:

1.  Magnet is present to create magnetic field.

2.  There is a coil placed in the magnetic field.

3.  Split rings are attached to rectangular coil. They are also called commutator. Commutator is a device which reverses the direction of flow of electric current through a circuit.

(a) Brushes touch the split ring.

(b) Battery is connected across the brushes.


Q.46 What changes are made in a commercial motor to make it more powerful? (3 Marks)

Following changes are made to make the commercial motor more powerful:

1. Number of loops are increased

2. Loop is wound around a soft iron core.

3. Electromagnet is used to create a strong magnetic field.

EMI

Q.47  What is electromagnetic induction? Explain how the movement of a magnet towards or away from a coil a galvanometer produces current?  (3 Marks)

When magnetic field changes in the region of a coil, a current flows in the coil. This phenomenon is called electromagnetic induction.

When a magnet moves close or far from a magnet, magnetic field in the region of the magnet changes. This changing magnetic field induces a current in the coil. Due to this current, galvanometer deflects.


Q.48  State Fleming’s right Hand Rule. (2 Marks)

In  Fleming's right  hand rule,  we arrange our fore finger, centre finger and thumb of our right hand  such that fore finger is in the direction of magnetic field, thumb is in the direction of motion of a straight wire, then centre finger would give the direction of induced current in the wire.


Q.49  Explain different ways to induce current in coil? (2 Marks)

The different ways to induce current in coil are:

1. Moving a permanent magnetic towards or away from the coil

2. Moving the coil towards or away from a permanent magnet.

Generator

Q.50  Give one important advantage of AC over DC? (1 Mark)

Transmission of AC over long distances is easier compared to DC.


Q.51 Give the principle, construction and Working of the AC Generator with a simple diagram. What modification will you suggest so that the output is DC? (5  Marks)

Principle:

When a straight wire is moved in magnetic field, induced current flows in it.

Alternating Current Generator

Construction:

1. Magnetic field is created using a magnet.

2. A rectangular loop of current carrying wire is placed in the magnetic field.

3. Two full rings are attached to the rectangular loop.

4. Two carbon brushes touch the two rings.

5. Both brushes form loop through galvanometer.

Working:

1. As wires of loop move in magnetic field, induced current flows in them due to EMI.

2. As wires of loop move upwards sometimes and sometimes downwards, the direction of current in the circuit changes. When an arm moves up during half revolution, current flow in one particular direction. When it moves down in other half revolution, current flows in other direction.

To convert AC generator to DC generator, full rings are replaced by split rings.


Q.52  What is essential difference in an a.c generator and d.c generator? (2 Marks)

1. AC generator produces alternating current which changes direction.But DC generator produces direct current which flows in a single direction.

2. AC generator used two full rings in its construction. But DC generator uses split rings.


Q.53  What is the frequency of A.C. supply in India? (1 Mark)

50 Hz


Q.54  What is the function of brushes in an electric generator? (1 Mark)

The function of brushes in an electric generator is to connect electric wires to the rings.


Q.55  Name and state the rule to find the direction of:  (5 Marks)

(a) Current induced in a coil due to its rotation in a magnetic field.

(b) Force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular.

(a) Fleming's Right Hand Rule: In  Fleming's right  hand rule,  we arrange our fore figure, centre finger and thumb of our right hand  such that fore finger is in the direction of magnetic field, thumb is in the direction of motion of a straight wire, then centre finger would give the direction of induced current in the wire.

(b) Fleming's Left Hand Rule: Arrange your fingers of left hand such that the fore finger points towards the direction of magnetic field and centre finger shows the direction of current, then the thumb will show the direction of force or motion.


Q.56  Name the phenomenon which is used in the production of electricity in a generator. (1 Mark)

Electromagnetic Induction


Q.57   Name one device which works on the phenomenon of electromagnetic induction. (1 Mark)

AC generator


Q.58   In what respect the construction of an A.C generator differs from that of a D.C generator? (2 Marks)

In case of DC generator, split rings are used instead of full rings and they make the current to flow in single direction.


Q.59   What type of generator is used at power stations? (1 Mark)

AC generators


Q.60   How does alternating current differ from the direct current? (2 Marks)

AC refers to Alternating Current. It changes the direction after equal intervals of time.

DC refers to Direct Current. It does not change its direction. It has only one direction.

 

Domestic Electric Circuit

Q.61  Give the circuit symbol for a fuse. Explain its importance in a circuit. (3 Marks)


Fuse is a very importance part of an electric circuit. It ensures that current in the circuit does not exceed a particular value so that the appliances in the circuit are not damaged.


Q.62  What is meant by earthing? Why should electrical appliances be earthed? (3 Marks)

The metallic bodies of appliances are connected to a wire which is finally connected to a large metallic plate placed deep in a pit on earth's surface. This process is called earthing.

Due to any problem in the electric circuit, the live wire may come in contact with the metallic body of an appliance. This can give electric shock to the person who touches the metallic body. So electrical appliances should be earthed.


Q.63  When does an electric short circuit occur? (2 Marks)

Short circuiting happens when live and neutral wires come in contact due to any defect such as breaking of insulation of wire due to heavy current flow.


Q.64 In which wire in a.c.housing circuit is the switch introduced to produce to operate the light? (1 Mark)

Live wire


Q.65 What is the usual color of the insulation of (a)live wire (b)neutral wire (c)earth wire? (3 Marks)

(a) Red (b) Green (c) Black


Q.66 What is the function of an earth wire? Why is it necessary to earth the metallic bodies of electrical appliances? (3 Marks)

The function of earth wire is to protect us from electric shock in case of any fault in the electric circuit or the electric appliance under use.

Sometimes, due to overloading or wear and tear, the insulation of live wire makes break. This exposes the high potential live wire in contact with the metallic body of the appliance. Now if someone touches the appliance, he may get electric shock. So to prevent such events, we need to do earthing.


Q.67  In household circuit, is a fuse wire connected in series or in parallel? (1 Mark)

In series


Q.68 What is the potential difference between live and neutral wire? (1 Mark)

220 V


Q.69 State the two ways by which electricity reaches our house. (2 Marks)

1. Through transmission wires over tall towers.

2. Through underground wires.


Q.70 What is the role of meter box,distribution box,ground wire,live wire and neutral wire? (5 Marks)

Meter box notes the amount of electricity used. The electricity bill is decided as per the reading of the meter box.

Distribution box divides the live and neural wires coming to house in two networks; one of 15A and the other of 5 A.

Ground wire protects us from electric shock in case of any fault in the electric circuit.

Live wire carries high potential to home.

Neutral wire completes the electric circuit coming to home so that current can flow in it.


Q.71 State two reasons for fuse in distribution box to melt. (2 Marks)

1. Overloading

2. Short-circuiting


Q.72 Why insulation of a wire can get damaged? (2 Marks)

Insulation of a wire can get damaged over time due to excessive use or due to overheating

as a result of high amount of current.


Q.73 What value of current (1 A, 6 A, 20 A) will be a good number for the following appliances (3 Marks)

(a) Fan        

(b) Electric iron          

(c) Geyser            

(d) small bulb        

(a) 6 A      

(b) 20 A          

(c) 20 A            

(d) 1 A


Q.74  Define the phenomenon overloading.

All the appliances use total current at a particular time exceeds the bearing capacity of that wire, the domestic wiring get heated. This Phenomenon is called overloading.

 

Value added questions:

Q.75 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. The direction of earth’s magnetic field is from G-south to G-north.

Let current is in direction of from west to east. So according to Fleming left hand rule force is vertically upwards.

(a) Reversing the direction of current, the direction of force will be reversed (vertically downwards).

(b) Doubling the magnitude of current.The magnitude of the force is doubled.


Q.76 In the straight wire A, current is flowing in the vertically downward direction whereas in wire B the current is flowing in the vertically upward direction. What is the direction of magnetic field:

(a) In wire A?           

(b) In wire B?

(a) According to Fleming right hand thumb rule, the direction of current in straight wire A is vertically downward so the direction of magnetic field around the wire A is clock wise.

(b) According to Fleming right hand thumb rule, the direction of current in straight wire B is vertically upward so the direction of magnetic field around the wire B is anti-clock wise.


Q.77 The magnetic field associate with a current-carrying straight conductor is in anti-clock wise 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?

If the conductor was held along the east-west direction and direction of magnetic field in straight wire is in anti-clock wise, then according to Fleming right hand thumb rule, the direction of current in wire is from east to west.


Q.78 A wire carrying current passes through the middle of the plane A perpendicular to it. If a magnetic needle is placed in the plane parallel to the wire. What will be the direction of the needle?

The direction of the needle along the tangent to a circle going anti-clockwise to an out coming current (to plane A).


Q.79 A wire carrying current passes through the middle of the plane A perpendicular to it. If a magnetic needle is placed in the plane perpendicular to the plane A, what will be the direction of the needle? 

Any direction, the needle is not deflected by a perpendicular field.


Q.80 A thick wire is hanging from a wooden table. An anti-clock wise magnetic field is to be produced around the wire by passing current through this wire by using a battery. Which terminal of the battery should be connected to the:

(a) Top end of wire?                      

(b) Bottom end of wire?

Give reason for your choice.

Current flows from battery in the direction of positive terminal to negative terminal and an anti-clock wise magnetic field is to be produced around the wire by passing current through this wire.For this situation current must flow in the wire from bottom to top.

- Top end of wire should be connected to negative terminal of the battery

- Bottom end of the wire should be connected to positive terminal of the battery.



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