GSEB Solutions for Class 10 Science and Technology – Magnetic Effects of Electric Current (English Medium)
Select the proper choice from the given multipule choices :
The direction of magnetic field lines in a region outside the bar magnet are——————-
A. From the N pole towards the S pole of a magnet.
Which of the following statements is false ?
D. The magnetic field lines can cross each other.
If the magnetic field lines cross each other, it would mean that magnetic field has two directions at that point, which is not possible. Hence, magnetic field lines can cross each other.
By which instrument the presence of magnetic field can be determined ?
D. Magnetic needle
Who had first observed the magnetic effect of an electric current ?
In 1891, a science teacher H.C. Oersted in Denmark first noticed that when electric current is passed through a conducting wire, magnetic field is produced around it.
With the help of which law the direction of a magnetic field can be decided ?
C. Right hand thumb rule
According to right hand thumb rule, whose direction is indicated by a thumb ?
A. Electric current
Definition of right hand thumb rule: If we hold the wire in right hand in such a way that the thumb points towards the direction of current then the curled fingers on the wire gives the direction of magnetic field.
The magnetic field produced in a straight conducting wire on passing the current through
C. circular around the wire
What is the field line of a magnetic field passing through the centre of current carrying circular ring ?
B. Straight line
At the centre of current carrying circular ring, the magnetic field lines are straight.
Whose magnetic field is like a magnetic field of a bar magnet ?
C. Current carrying solenoid
The magnetic field lines resulting from a current carrying solenoid is same as that due to a bar magnet.
Who gave the principle of electromagnetic induction ?
The principle of electromagnetic induction was given by Michael Faraday in 1831.
Which is the direction of magnetic force acting on a current carrying wire placed in a magnetic field ?
C. Perpendicular to magnetic field
The direction of force acting on a current carrying wire placed in a magnetic field is given by Fleming’s left hand rule. It is always perpendicular to the direction of electric current and magnetic field.
How is a current carrying wire placed in a magnetic field so that magnetic field does not act on it?
A. Parallel to the magnetic field
When the current carrying wire is placed in such a way that the direction of current is in the direction of magnetic field or in the opposite direction, no force is exerted on it.
From which of the following cases, the induced current in the loop will not be obtained ?
D. The loop and the magnet are moved in one direction with the same speed.
In this case, magnetic flux linked with the loop does not change, and hence induced current shall not be obtained.
Which instrument is used in converting electrical energy into mechanical energy ?
B. Electric motor
Electric motor is a device which converts electrical energy into mechanical energy.
On which principle does the electric generator work ?
C. Mechanical energy is converted into electrical energy.
An electric generator works on the principle of electromagnetic induction.
The magnitude of an AC voltage used in India is———————— and the frequancy is———–
C. 220 V, 50 Hz
Which coloured wire is used for earthing ?
Green coloured wire is used for earthing.
Which type of current is obtained from a battery ?
A. DC current
The current obtained from a battery is direct current and it flows from the positive terminal to the negative terminal of the battery through an appliance. Its magnitude and direction remains constant with time.
Which instrument is used to know the presence of an electric current ?
A fuse wire is———————————–
A fuse wire allows current to pass through it. So, it is a conductor.
———————— rule is used to know the direction of an induced current in the circuit.
B. Fleming’s right hand
Stretch the forefinger, middle finger and the thumb of the right hand at right angles to one another. Adjust the forefinger in the direction of magnetic field, and the thumb pointing in the direction of motion of conductor. The direction of the middle finger will indicate the direction of induced electric current.
How many times does an AC electric current with the frequency 50Hz change its direction ?
At the center of which of the following four circular rings has maximum magnetic field while passing equal current through each one ?
The magnitude of magnetic field decreases inversely at a distance while moving away from a conducting wire. Circle one (A) has minimum radius, hence magnetic field at its centre is maximum.
Answer the following questions in brief :
Give the characteristics of magnetic field lines.
Characteristics of magnetic field lines are as follows:
- Magnetic field lines form closed loops. They start from North Pole and reach to the South Pole.
- The magnetic field region where the lines are closer are stronger compared to the regions where the magnetic field lines are far apart.
- The tangent drawn at any point of the magnetic field line gives the direction of the magnetic field at that point.
- Magnetic field lines do not intersect each other.
Explain the ‘right hand thumb rule’ to know the direction of magnetic field.
Right hand thumb rule: If we hold the wire in right hand in such a way that the thumb points towards the direction of current then the curled fingers on the wire gives the direction of magnetic field.
What will happen while placing a current carrying conductor in a magnetic field ? Explain.
When a current carrying conductor is placed in a magnetic field, it experiences a force.
When electric current flows through the conductor, a magnetic field is produced around it. During the interaction between the magnetic field of this conductor and the magnetic field of the magnet, the wire and magnet exert equal and opposite forces on each other. The magnet being heavy remains stationary and the wire moves due to this force.
By which law can the direction of an induced electric current can be determined ? Give the explanation of that law.
Fleming’s right hand rule gives the direction of an induced electric current.
Stretch the forefinger, middle finger and the thumb of the right hand at right angles to one another. Adjust the forefinger in the direction of magnetic field, and the thumb pointing in the direction of motion of conductor. Then, the direction of middle finger indicates the direction of the induced electric current.
Explain the provision of an earthing wire.
Every household circuit is provided with an earthing wire. This wire is connected with a metal placed and dumped deep near the house. Whenever there is leakage of current in any appliance, it reaches the metallic surface of the appliance and through the earthing wire which is connected to the metallic surface of these appliances, the leaked current goes directly to the ground.
Mention the usefulness of a fuse in a domestic electrical circuit.
A fuse is connected in series with an electric circuit to avoid over loading and short circuits.
When the current in the circuit exceeds its specified limit, excess heat is produced which melts the fuse wire immediately. Thus, the circuit gets broken and no current passes through it. This prevents other appliances as well as circuit from getting damaged.
Write Answers of the following questions :
Discuss the magnetic field resulting from a current carrying circular ring.
The magnetic field produced from a current carrying loop is as shown in the figure below.
The field lines are circular near the wire. These circles get enlarged while moving away from wire. Near the centre of the loop, the lines almost become straight and are placed very close to each other, such that the magnetic field is stronger at the centre. The direction of magnetic field can be determined by the right hand thumb rule. The field at the centre is directly proportional to the current passing through the loop as well as the number of turns in the coil and inversely proportional to the radius of the ring.
What is a solenoid ? Give the charcteristics of magnetic field resulting from solenoid.
A construction like a coil made by a conducting wire wound closely and separately in form of a cylinder is called a solenoid.
The magnetic field resulting from solenoid is shown in the figure above. It is same as that due to a bar magnet. Thus, one end of the solenoid behaves as North Pole and the other end as South Pole. In the inner region of a solenoid, the field lines are parallel indicating that the magnetic field is uniform at every point inside the solenoid.
The strength of the magnetic field produced by a solenoid is directly proportional to the number of turns on the solenoid and the current passing through it.
What precautions should be taken during the use of electricity ?
Safety measures while using electricity:
- One must use wires of current carrying capacity higher than the total current which can flow through the circuit when using all the appliances to avoid over heating of the circuit.
- The fuse must be connected to the main meter box, all the wiring in the house and to each appliance so as to prevent short-circuiting.
- The insulation of the wires must be of good quality to avoid electric shocks.
- Electrical appliances such as switch, socket, electric wire etc. should not be operated with wet hands and should always be kept in dry condition.
Answer the following questions in pointwise :
Describe the experiment that explains the phenomenon of an electromagnetic induction and give its conclusions.
i. Make a circular loop of conducting wire and connect a galvanometer with it to record the presence of electric current, as shown in figure below.
ii. Take a bar magnet and keep it stationary near the loop. The galvanometer does not show any deflection (fig a), which means no current is produced in the loop.
iii. Next, move the North pole of the magnet rapidly towards the loop. The galvanometer deflects to one side showing the presence of electric field (fig b).
iv. Then take the magnet away from the loop rapidly. Again the galvanometer shows deflection indicating the presence of current, but in opposite direction (fig c).
v. In the same way if South Pole of the magnet is taken, the deflection in the galvanometer will be opposite to both the above mentioned cases.
From the above observation it is clear that whenever there is a relative motion between the coil and the magnet, a current is induced in the coil due to change in the magnetic flux linked with it.
This phenomenon is known as electromagnetic induction.
Write a short note on electric bell.
The electric bell works on the principle of electromagnet. Its construction is shown in the figure below:
It is made up of an electromagnet, a bell (metallic cup), a soft iron strip (which works as a hammer) and a contact screw.
When current is passed through the circuit, the electromagnet acts like a magnet and attracts the iron strip. The iron strip (hammer) being elastic, strikes the bell. Simultaneously, its contact with the screw is broken and the circuit breaks and current stops flowing through the electromagnet. As such the iron strip comes back to its original position and again the current passes through the electromagnet.
This phenomenon happens many times in a second and as the hammer strikes the bell, the sound is heard. The bell rings until the circuit is switched off.
Electric bell is used in school, at offices, home, alarms etc.
Describe domestic electric circuit with the help of a diagram..
Below is the diagram of domestic electric circuit:
From the power station, electricity is supplied to our houses at 220V. The electric line is connected to the meter-box in a house through a fuse of high rating (company fuse). In the main switchboard, fuses are kept for different circuits as per requirement. Through the main switch they are connected to the line wires in the house.
These wires carry two different values of current in the house:
15 A current line is connected to the appliances of higher power ratings like geyser, air conditioner, etc.
5A current line is connected to appliances of low power rating like tube light, television, etc.
Besides, another important aspect of domestic electric circuit is earthing. The earthing wire is connected with the metal plate and dumped deep near the house.
In a domestic electric circuit, red coloured wire is used as live wire, black coloured wire as neutral wire and green coloured wire as earthing.
Answer the following questions in detail :
Describe the principle, construction and working of an electric motor along with a figure.
Construction: It consists of a loop ABCD of an insulated copper wire placed in a permanent magnetic field such that AB and CD remain perpendicular to the magnetic field. The ends of the wire are connected to two semicircular rings. The inner part of both the rings is insulated. The rings are attached on an axle such that they can rotate easily on it. The outer position of the ring is in contact with stationary brushes which in turn are connected to an external circuit.
Working: The plane of the coil is horizontal and the split ring S1 touches the brush B1 while the split ring S2 touches the brush B2. The brush B1 is connected to the anode of the d.c. battery while the brush B2 is connected to the cathode. The current flows in the coil in the direction ABCD. The arms BC and DA being parallel to the magnetic field experience no force.
According to Fleming’s left hand rule, force ‘F’ acting on the arm AB, is inward and perpendicular to the plane of the coil and the force on the arm CD is in just in the opposite direction. The forces on the arms AB and CD being equal and opposite form an anticlockwise couple, due to which the coil begins to rotate. It rotates in such a way that the arm AB goes in and the arm CD comes out.
When the coil reaches the vertical position, the couple becomes zero since the forces on the arms now become collinear. However, due to the inertia of motion, the coil does not stop in this position. As the coil passes from the vertical the split ring S1 comes in contact with the brush B2, while the split ring S2 comes in contact with the brush B1. Now the current flows through the coil in the direction DCBA and the forces acting on the arms DC and AB of the coil again form an anticlockwise, couple due to which the coil remains rotating in the same direction. Thus, whenever the coil comes in the vertical position, the direction of the current through the coil reverses and the coil continues to rotate in the same direction.
Describe the principle, construction and working of an electric generator with a figure.
Principle: Electric generator works on the principle of electromagnetic induction. It converts mechanical energy into electrical energy.
Construction: A loop ABCD is rotated in a permanent magnetic field. Its ends are connected with two semi-circular rings as shown in the figure below. These rings are insulated from each other and can slide while remaining in contact with brushes X and Y. A galvanometer is connected between the two ends of brush.
Working: On rotating the loop in a magnetic field, the side AB moves upward and the side CD moves downwards. Thus, the magnetic flux linked with the loop changes and a current is induced in it whose direction can be determined by the Fleming’s right hand rule. In the figure, current is flowing through the path B-A-G-D-C.
After half rotation, the ring P comes in contact with the brush Y and the ring Q with the brush X. Thus, the brush X is always in contact with the side moving upwards and the brush Y is always in contact with the side moving downwards because of which the current flows in one direction. This current is called direct current. This type of a generator is called a DC generator. Similarly, instead of half ring if full ring is used, then A.C. current can be generated and such a generator is called A.C. generator.