CBSE Class 10 Science Magnetic Effects of Electric Current Assignment Set G

Very Short Answer Type Questions :

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

Question. State the direction of magnetic field in the following case:

Answer: Direction is out of the page.

Question. A coil made of insulated copper wire is connected to a galvanometer. What will happen to the deflection of the galvanometer if this coil is moved towards a stationary bar magnet and then moved away from it?
Give reason for your answer and name the phenomenon involved.
Answer: In both the case there is a change in magnetic field associated with the coil, an induced current is produced in the coil, but in opposite direction. This phenomenon is called electromagnetic induction (EMI).

Question. State two ways by which the strength of an electromagnet is increased. 
Answer: (i) Increase in number of turns in the solenoid.
(ii) Increase in the strength of current flowing in the solenoid.

Question. Suggest one way to distinguish a wire carrying current from a wire carrying no current.
Answer: The magnetic compass needle will get deflected near the wire current carrying but not near the wire with no current.

Question. Give two uses of electromagnets.
Answer: (i) It is used in cranes for lifting heavy loads.
(ii) used in electric bells.

Question. What type of core is used to make an electromagnet?
Answer: Soft iron core is used in making an electromagnet.

Question. State the direction of the magnetic field inside the bar magnet.
Answer: In a magnet, magnetic field lines goes from S pole to N pole.

Question. Name two safety measures commonly used in electric circuits and appliances.
Answer: Two safety measures are:
(a) use of earth wire and proper earthing.
(b) use of fuse.

Question. Name some devices in which electric motors are used.
Answer: Electric motors are used in all devices where we want to convert electrical energy into Mechanical energy. In our houses, electric motors, coolers, mixer grinders, washing machines, computers etc motor is used.
(a) use of earth wire and proper earthing.
(b) use of fuse.

Question. Why are magnetic field lines form closed curves?
Answer: It is because outside the magnet, magnetic field lines start from north pole and merge at south pole whereas inside the magnet they start from south pole and merge at north pole, therefore these lines from closed curves.

Question. 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 wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?
Answer: The direction is vertically downwards.

Question. Which property of a proton will change while it moves freely in a magnetic field?
Answer: Momentum or Velocity.

Short Answer Type Questions :

Question. For the circular coil carrying current shown below draw magnetic field lines. Decide which of its face behaves as north pole and which face behaves as south pole. Give reason to justify your answer
Answer: Front face behaves like a north pole as field emerges out of it. Rear face behaves as south pole as field enters into this face.

Question. 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?
Answer: (i) When a bar magnet is pushed into the coil of insulated copper wire connected to a galvanometer, galvanometer gives a deflection towards left.
(ii) When the bar magnet is withdrawn from inside the coil, again an induced current is set in coil that deflect the galvanometer towards right.
(iii) If the bar magnet is held stationary inside the coil, then no induced current is set and galvanometer does not show any deflection.

Question. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220V) that has a current rating of 5.A. What result do you expect? Explain.
Answer: Power rating of electric oven (P) = 2 kW = 2000 W
Current drawn (I) = P/V = 2000/220 = 9.09 A.
As the current rating of domestic electric circuit is only 5A the oven draws a current of 9.09 A. Which is more than the current rating; hence the circuit will be damaged due to overheating/overloading.

Question. (a) What is the standard colour code followed for
(i) live
(ii) neutral and
(iii) earth wires used in electric circuits?
(b) Which part of an electric appliance is earthed and why?
Answer: (a) The standard colour code for
Live wire – Red
Neutral – Black
Earth – Green respectively.
(b) The metallic case of an electrical appliance is earthed because metals are good conductors of electricity and in case if current exceeds i.e. live wire touches the metallic case of an appliance and then due to earthing all the excess amount of current flows down to the earth and we prevent ourselves from an electric shock.

Question. 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 Side 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 left opposite to that in case one).
(iii) As it is stationary no change in magnetic flux linked with coil, so galvanometer shows no deflection.

Question. In activity 13.7, how do we think the displacement of rod AB will be affected if
(i) current is rod AB is increased,
(ii) a stronger horse shoe magnet is used, and
(iii) length of the rod AB is increased?
Answer: (i) O increasing the current in rod AB its displacement will increase.
(ii) If stronger horse-shoe magnet is used then the displacement of rod AB will increase.
(iii) If length of the rod is increased, force acting on it will increase and hence, displacement of the rod increases.

Question. (a) Define the term current rating of an electric fuse?
(b) Name the material used to make electric fuse?
(c) Name two safety measure commonly used in electric circuit and appliances?
Answer: (a) The maximum amount of current that can be passed through the fuse wire without melting it.
(b) Copper or alloy of lead acid tin.
(c) Electric fuses and earth wire.

Question. Consider a circular wire lying in the plane of the table and the direction current in it is antilock wise.
(i) Draw the magnetic field lines produced around it.
(ii) Why does magnetic field at the center of current carrying circular loop appear straight? Explain with diagram.
Answer: (i)

(ii) Because of large curvature of magnetic field lines at centre.

Question. What is a solenoid? Draw magnetic field lines showing the magnetic field inside and outside the current carrying solenoid?

Answer: A solenoid is a coil of many turns of insulated copper wire closely wound in the shape of a ring.

Question. State the consequences that can lead to a short circuit.
                                          Or
One of the major cause of fire in office building is short circuiting. List three factors which may lead to the short circuit.
Answer: It occurs as a consequence of failure of electrical insulation’s due to which live wire comes in direct contact with neutral or earth wire. presence of external conducting material such as water which is introduced accidentally into the circuit. electrical appliances are forced to operate when its moving parts are jammed. connection of current carrying parts of electrical equipment’s comes in contact to one another due to human or natural cause and use of less rating wires. When this happens, there is an excessive electric current which can damage the circuit and may also cause electrical fires.

Question. Define a solenoid. Compare the magnetic field produced by a solenoid with that of a bar magnet. 
Answer: A coil of many circular turns of copper wire wrapped in the shape of a cylinder, is called a solenoid.The magnetic field lines in a solenoid, through which current is passed, is very similar to that of a bar magnet. One end of the coil acts like the magnetic north pole, while the other acts like the magnetic south pole. The magnetic field produced by a long solenoid has all the properties of the field produced by a bar magnet.

Question. List the properties of magnetic lines of force.
Answer: Properties of magnetic field lines of force as follows:
a. Outside a magnet, the field lines are directed from N-pole of magnet towards S-pole and inside the magnet lines are directed form S-pole to N-pole.
b. Magnetic field lines are closed curves.
c. No two magnetic field lines intersect each other.
d. Relative strength of magnetic field lines is given by degree of closeness of the filed lines.

Question. 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.

Answer: Current drawn by electric oven
Current rating of the circuit = 5 A
So, fuse will blow off and power supply will cut off

Question. What precaution should be taken to avoid the overloading of domestic electric circuit?
Answer: We should take following precaution to avoid the overloading of domestic electric circuit:
(a) Two separate circuits should be used, one of 5A current rating of bulbs, fans, tubes etc. and the other 15 A current rating for appliances with higher current rating such as geysers, air coolers, electric iron, electric stoves etc.
(b) Too many appliances should never be connected to a single socket.
(c) A fuse of appropriate current rating should be used with the electric circuit.

Question. Distinguish between a bar magnet and an electromagnet.
Answer: 

Question. (a) Mention the factors on which the direction of force experienced by a current carrying conductor placed in a magnetic field will depend.
(b) Under what conditions is the force experienced by a current carrying conductor placed in a magnetic field maximum?
(c) A proton beam is moving along the direction of a magnetic field. What force is acting on proton beam? 
Answer: (a) (i) direction of current, (ii) direction of magnetic field.
(b) When direction of current is perpendicular to the direction of magnetic field, the force experienced will be maximum.
(c) No, force is exerted by a proton beam because proton beam is moving along the direction of magnetic field.

Question. Why does a compass needle get deflected when brought near a bar magnet?
Answer: The compass needle is small bar magnet. When a compass needle is brought near a bar magnet then due to repulsive force between unlike poles and attraction between unlike poles, the compass needle is deflected and settle in the direction of net magnetic field.

Question. 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 floe of floe of current (b) doubling the magnitude of current.
Answer: The direction of earth’s magnetic field is from U-south to 0-north. Let current is from west to east. Therefore, force is vertically upwards.
(a) By reversing the direction of current, the direction of will be reversed i.e. vertically downwards.
(b) The magnitude of the force is doubled.

Question. Explain the underlying principle and working of an electric generator by drawing a labeled diagram. What is the function of brushes?
Answer: Electric generator labelled diagram is as follows:
Principle: An electric generator works on the principle of electromagnetic induction.
Working: Let the in the beginnings brushes B1 and B2 are kept pressed separately on rings R1 and R2 respectively. Let the axle attached to the rings is rotated such that arm AB of the coil moves up and arm CD moves down in the magnetic field. Due to rotation of arms AB and CD induced current are set up in them. As per Fleming’s right hand rule, induced current in these arms along the directions AB and CD respectively and current flows into B1 and B2. After half rotation, arm AB moves downward and arms CD upward to change the direction opposite to first case. Thus, after every half rotation current changes its direction and an alternate current is obtained in the generator. Brushes are kept pressed on the two slip rings separately. Outer ends of the brushes are connected to the galvanometer. Thus, brushes help in transferring current from the coil
ABCD to external circuit.

Question. List three sources of magnetic field.
Answer: (i) Magnetic field is associated with bar magnet
(ii) A current carrying conductor produces magnetic field.
(iii) A current carrying curricular loop also produces magnetic field.

Question. (a) Write the values of the following physical quantities in connection with domestic power supply in our country: (i) potential difference between live wire and neutral wire. (ii) frequency of ac.
(b) Explain the role of the following as safety measure in domestic electric appliance/circuits: (i) earth wire (ii) fuse.
Answer: (a) (i) 220 V, (ii) 50 Hz
(b) Safety measure in electric appliance/circuits:
(i) Earth wire is a safety device to protect us from electric shock due to leakage of current or faulty electric appliances. An earth wire is a thick copper wire connected to a metal plate buried deep in the earth. The metallic body of the electric appliance is connected to the earth wire, it provides a low resistance conducting path and leaked current goes to deep in the earth and human beings do not get a fatal electric shock.
(ii) Fuse: It is also a safety device. It is a wire of an alloy with low melting point. If a current greater than a particular values flows in the circuit it will melt and circuit is broken and stops power supply in the circuit.

Question. We know a current carrying conductor placed in a magnetic field experiences a force due to which the conductor moves. How do we think the rod displaces if-
(a) current in rod is increased
(b) a stronger horse shoe is inserted
(c) length of the rod is increased.
Answer: Force acting on current carrying conductor F = BIL
(a) When I increase, F also increases hence displacement of the rod increases.
(b) When a stronger horse shoe magnet is inserted, magnetic field B increases. So force F increase. Hence displacement increases.
(c) When I increase, force increases and hence displacement increases.

Question. Current- time graph from two different sources are shown in the figure.

(i) Name the type of current shown by graph (A) and (B)?
(ii) Name any one source of shown by (A) and (B)?
(iii) What is frequency of current in case (B)?
(iv) Write two difference between current shown by (A) and (B)?
Answer: (i) Graph A represent D.C. and graph B represent A.C.
(ii) Source of (A) – Dry cell
Source of (B) – A.C. generator
(iii) For graph (B) f = I/T = 1/0.02
f = 50Hz
(iv) 1

Question. A coil of insulated wire is connected to a galvanometer.
Explain what happens if a bar magnet with its north pole towards one face of the coil is:
a. moved quickly towards the coil,
b. kept stationary inside the coil, and
c. moved quick away from the coil?
Answer: When a bar magnet is moved towards the coil there is change in magnetic field in
a. coil so a current is induced in the coil so galvanometer gives a deflection.
b. when magnet is kept stationary in the coil then due to no change in the magnetic field no current is induced in the coil.
c. when magnet is moved quickly away from the coil again there is change in magnetic field associated with the coil so again a current is induced but in the opposite direction.

Question. (a) Name four appliances wherein an electric motor is used as an important component. In what respect it is different from generator?
(b) Define the terms used in the generator
(i) armature
(ii) slip rings
(iii) brushes
Answer: (a) The four appliances which have electric motor inside them are
(i) Mixers (ii) Washing machine (iii)Refrigerators (iv) Blenders
(b) (i) Armature – Armature is a coil of large number of turns of insulated copper wire wound over a soft iron core.
(ii) Slip rings- Slip Rings one two rings made up of brass which rotates along with the coil.
(iii) Brushes- Brushes are made up of carbon which are pressed against the slip rings and are connected to external circuit where output is obtained.

Question. State one main difference between A.C and D.C. Why A.C is preferred over D.C for long range transmission of electric power? Name one source each of D.C and A.C.
Answer: Difference between A.C. and D.C. The alternating current (A.C.) reverses its direction periodically whereas the direct current (D.C.) always flows in one direction.
A.C. is preferred over D.C. because it can be transmitted over long distance without much loss of energy.
D.C. source : Battery A.C. source : A.C. generator

Question. (a) State Fleming’s left hand rule.
(b) Write the principle of working of an electric motor.
(c) Explain the function of the following parts of an electric motor.
(i) Armature, (ii) Brushes, (iii) Split ring
Answer: (a) Fleming’s left hand rule: If we stretch thumb, forefinger and middle finger of left hand perpendicular to each other in such a way that forefinger points in the direction of magnetic field, middle finger points in the direction of current then the thumb will point in the direction of motion/force on the current carrying conductor.
(b) Principle of working of electric motor: A current carrying coil placed in a magnetic field experience a torque. If the coil is free to move it will rotate in the magnetic field.
(c) (i) Armature: The soft iron core on which the coil is wound along with coils is called armature which enhances the power of motor.
(ii) Brushes: Brushes help in transfer of current between coil and external circuit.
(iii) Split rings reverses the direction of current after every half rotation of the coil so that the direction of torque/force on the coil remains and it continuous to rotate.

Question. What is meant by overloading of an electrical circuit?
Explain two possible causes due to which overloading may occur in household circuit. Explain one precaution that should be taken to avoid the overloading of domestic electric circuit.
Answer: Connecting large number of electric appliances in one socket whose load is more than the maximum permitted limit. The two possible cause are
a. all of a sudden supply of high voltage and
b. too many devices connected in a single socket.
Precautions:
a. use of voltage regulator,
b. load of a socket must be greater than its permitted rating.

Question. How will the magnetic field produced in a current carrying circular coil changes, if we increase the:
a. value of current flowing through it?
b. distance of point P from the coil?
c. number of turns of the coil?
Answer: a. Magnetic field is directly proportional to current so magnetic field increases when current increases.
b. If we increase the distance of point P, magnetic field decreases.

c. On increasing the number of turns magnetic field increasing.

Question. Draw a diagram to show how a magnetic needle deflects when it is placed above or below a straight conductor carrying current depending on the direction of the current in the conductor.
Answer: 

Long Answer Type Questions :

Question. Draw the pattern of lines of force due to a magnetic field through and around a current carrying loop of wire. How would the strength of the magnetic field produced at the centre of the circular loop be affected if
a. the strength of the current passing through this loop is double?
b. the radius of the loop is reduced to half of the original radius?
Answer: The pattern of lines of force due to a magnetic field through and around a current carrying loop of wire is shown below

a. Strength of magnetic field is doubled when the current through the loop is doubled B α I .
b. Strength of magnetic field is doubled when the radius of the loop is halved B α 1/F

Question. (a) Describe an activity to draw a magnetic field line outside a bar magnet from one pole to another.
(b) List any two properties of magnetic field lines.
Answer: (a) Fix a plane white drawing sheet on a drawing board. Now take a bar magnet and a compass. Place the magnet at the middle of the paper and mark its boundary with the help of pencil. Now place compass near N-pole of bar magnet and the position of needle of the compass. Now move the compass on the drawing board coinciding S-pole of the compass with the previous marked point of N of the needle and so on move forward from one end (N-pole) to the S-pole of the bar magnet. Join all the marked points. You will get magnetic lines of force.

(b) Properties of magnetic field lines.
(i) Magnetic field lines do not intersect each other.
(ii) Magnetic field lines emerge out at N-pole and goes to the S-pole whereas in magnet these travel from S-pole to N-pole.

Question. In our daily life we use two types of electric current whose current-time graphs are given below:

a. Name the type of current in two cases.
b. Identify any one source for each type of current.
c. What is the frequency of current in case (b) in our country?
d. On the basis of these graphs list two differences between the two currents.
e. Out of the two which one is used in transmitting electric power over long distances and why?
Answer: a. (i) DC (ii) AC

b. (i) cell, (b) AC generator
c. 50 c/s or 50 Hz.
d. (i) Magnitude of DC is constant magnitude of AC is varying
(ii) DC is unidirectional ac changes its direction after a fixed period.
e. AC can be transmitted by changing it at high voltage with the help of transformer to minimise loss in transmission.