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

Question: Choose the incorrect statement from the following regarding magnetic lines of field
a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points.
b) Magnetic field lines are closed curves.
c) If magnetic field lines are parallel and equidistant, they represent zero field strength.
d) Relative strength of magnetic field is shown by the degree of closeness of the field lines.
Answer: c

Question: Which of the following correctly describes the magnetic field near a long straight current carrying wire?
a) The field consists of straight lines perpendicular to the wire.
b) The field consists of straight lines parallel to the wire.
c) The field consists of radial lines originating from the wire.
d) The field consists of concentric circles centered on the wire.
Answer: d

Question: The strength of magnetic field inside a long current carrying straight solenoid is
a) More at the ends than at the centre
b) Minimum in the middle
c) Same at all points
d) Found to increase from one end to the other
Answer: c

Question: A positively-charged particle (alpha–particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
a) Towards south
b) Towards east
c) Downward
d) Upward
Answer: d

Question: 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
a) Two revolutions
b) One revolution
c) Half revolution
d) One-fourth revolution
Answer: c

Question: The phenomenon of electromagnetic induction is
a) The process of charging a body
b) The process of generating magnetic field due to a current passing through a coil
c) Producing induced current in a coil due to relative motion between a magnet and the coil
d) The process of rotating a coil of an electric motor
Answer: c

Question: For a current in a long straight solenoid N- and S-poles are created at the two ends. Among the following statements, the incorrect statement is
a) The field lines inside the solenoid are straight showing uniform field
b) The strong magnetic field produced inside the solenoid can be used to magnetise soft iron placed inside
c) The pattern of the magnetic field associated with the solenoid is different from the bar magnet
d) The N and S-poles exchange position when current direction is reversed
Answer: c

Question: Which property of a proton can change while it moves freely in a magnetic field?
a) Mass
b) Speed
c) Velocity
d) Momentum
Answer: c,d

Assertion and Reason Based MCQs :

Directions : In the following questions, A statement of Assertion (a) is followed by a statement of Reason (R).
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is NOT the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is true.

Question: Assertion (a): In Fleming’s Left Hand Rule, the direction of magnetic field, force and current are mutually perpendicular.
Reason (R): Fleming’s Left hand Rule is applied to measure the induced current.
Answer: c

Question: Assertion (a): An alpha particle placed in a magnetic field will not experience any force, if it moves in the magnetic field parallel to field lines.
Reason (R): The force is zero if current and field are in the same direction.
Answer: a

Question: Assertion (a): Two bar magnets attract when they are brought near to each other with the same pole.
Reason (R): Unlike poles will attract each other.
Answer: d

Question: Assertion (a): Magnetic field lines never intersect.
Reason (R): At a particular point magnetic field has only one direction.
Answer: a

Very Short Answer Type Questions :

Question: What is meant by magnetic field ?
Answer: The region surrounding a magnet in which the force of the magnet can be detected is said to be its magnetic field.

Question: Why does a compass needle show deflection when brought near a current carrying conductor ?
Answer: Due to production of magnetic field around the current carrying conductor.

Question: The change in magnetic field lines in a coil is the cause of induced electric current in it. Name the underlying phenomenon. 
Answer: Electromagnetic induction.

Question: Why are magnetic field lines more crowded towards the pole of a magnet ? 
Answer: The magnet is stronger at the poles so the magnetic field lines are crowded at the poles.

Short Answer Type Questions :

Question: Name, state and explain with an example the rule used to determine the direction of force experienced by a current carrying conductor placed in a uniform magnetic field. 
Answer: Fleming’s Left Hand Rule: The direction of force which acts on the current carrying conductor placed in a magnetic field is given by Fleming’s left hand rule. It states that if the forefinger, thumb and middle finger of left hand are stretched mutually perpendicular and if the forefinger point along the direction of external magnetic field, middle finger indicates the direction of current, then thumb points along the direction of force acting on the conductor.
Example: When an electron enters a magnetic field at right angles, the direction of force on electron is perpendicular to the direction of magnetic field and current according to this rule.

Question: Give reasons for the following:
(i) There is either a convergence or a divergence of magnetic field lines near the ends of a current carrying straight solenoid.
(ii) The current carrying solenoid when suspended freely along a particular direction.
(iii) The burnt out fuse should be replaced by another fuse of identical rating. 
Answer: (i) Divergence or degree of closeness of magnetic field lines near the ends of a current carrying straight solenoid indicates a increase in the strength of the magnetic field near the ends of the solenoid.
(ii) A current carrying solenoid acts as a bar magnet.
We know that a freely suspended bar magnet aligns itself in the North-South direction. So, a freely suspended current carrying solenoid also aligns itself in the North-South direction. 
(iii) Burnt out fuse cannot be re-used. Also, a fuse wire works because of its lower melting point. If the fuse with larger rating is used with an appliance, the fuse wire shall not melt and hence would fail to serve the required purpose. So, new fuse of same rating should be used for electrical safety.

Question: Can a freely suspended current carrying solenoid stay in any direction ? Justify your answer. What will happen when the direction of current in the solenoid is reversed ? Explain.
Answer: A current carrying solenoid behaves like a magnet.
When suspended freely, it will stay in north – south direction.
On reversing current its polarity will be reversed and so it will turn at 180°.

Question: State any two factors on which the magnetic field produced by a current carrying straight conductor depends.
Mention the rule which helps to find the direction of its magnetic field.
Answer: Factors on which the magnetic field produced by a current carrying conductor depends:
(i) Strength of current passing through the conductor. 
(ii) Distance of the point of measurement from the conductor. 
Right Hand Thumb Rule gives the direction of magnetic field.

 Question: What is meant by solenoid ? How does a current carrying solenoid behave ? Give its main use.
Answer: Solenoid is a closely wound cylindrical coil of insulated metallic wire wrapped closely in the shape of a cylinder. A current carrying solenoid behaves as an electromagnet. The uniform magnetic field inside it may magnetise a steel rod permanently.

Question: An alpha particle is placed in a magnetic field.
Will it experience any force, if: 
(i) it moves in the magnetic field parallel to field lines?
(ii) it moves in the magnetic field perpendicular to field lines? 
Answer: (i) No, because, the force is zero if current and field are in the same direction.
(ii) Yes, because, the force is maximum when current and magnetic field are perpendicular.

Long Answer Type Questions :

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 as electric motor.
(i) Armature (ii) Brushes (iii) Split ring
Answer: (a) Fleming’s left-hand rule: Stretch the forefinger, middle finger and thumb of left hand in such a way that they are mutually perpendicular to each other. If the forefinger points in the direction of magnetic field, middle finger points in the direction of current then the thumb shows the direction of force or motion on the current carrying conductor.
(b) Principle of working of electric motor: A coil carrying electric current placed in an external magnetic field experiences a force.
(c) (i) Function of armature : It is a rectangular iron core wrapped by the copper coil through which electricity passes and due to magnetic field it experiences a force and rotates.
(ii) Function of brushes: It helps in easy transfer of charge between the coil and the external circuit.
(iii) Function of split rings: It reverses the direction of current after each half rotation of the coil so that the coil can keep rotating continuously.

Question: (i) A coil of insulated copper wire is connected to a galvanometer. What happens if a bar magnet is:
(a) Pushed into the coil ?
(b) Withdrawn from inside the coil ?
(c) Held stationary inside the coil ? Give reasons for your observation.
(ii) Mention one more method of inducing current in a coil. 
Answer: (i) (a) When a bar magnet is pushed into the coil of insulated copper wire connected to a galvanometer, an induced current is set-up in the coil due to charge of magnetic field through it. As a result, galvanometer gives a deflection (say towards left) and returns to original position. 
(b) When the bar magnet is withdrawn from inside the coil, again an induced current is set up in the coil due to charge of magnetic field through it. As a result galvanometer gives a deflection in the reverse direction (say towards right) and returns to original position. 
(c) If the bar magnet is held stationary inside the coil, then there is no induced current in the coil, because there is no change in magnetic field through it. As a result, galvanometer does not show any deflection. 
(ii) By changing current in another coil placed near it. 

Question: (a) What are magnetic field lines ? How is the direction of magnetic field at a point in a magnetic field determined using field lines ?
(b) Two circular coils ‘X’ and ‘Y’ are placed close to each other. If the current in the coil ‘X’ is changed, will some current be induced in the coil ‘Y’ ? Give reason.
(c) State ‘Fleming’s right hand rule”.
Answer: (a) Magnetic field line: Path along which a hypothetical free north pole would tend to move. 
Direction of magnetic field are a point is determined by drawing a tangent to the magnetic field line at that point With change in current in the coil X, the magnetic field associated with it also changes around the coil Y placed near it. This change in magnetic field induces a current in the coil Y. 
(c) Fleming’s right hand rule Stretch the thumb, forefinger and middle finger of right hand so that they are perpendicular to each other. If the forefinger indicates the direction of the magnetic field and the thumb shows the direction of motion of the conductor, then the middle finger will show the direction of induced current in the conductor.