Magnetic Effect of Electric Current
NCERT Exemplar Solution
MCQs
Question 1: Choose the incorrect statement from the following regarding magnetic lines of field
- 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
- Magnetic field lines are closed curves
- If magnetic field lines are parallel and equidistant, they represent zero field strength
- Relative strength of magnetic field is shown by the degree of closeness of the field lines
Answer: (c) If magnetic field lines are parallel and equidistant, they represent zero field strength
Question 2: If the key in the arrangement (Given figure) is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are
- Concentric circles
- Elliptical in shape
- Straight lines parallel to each other
- Concentric circles near the point O but of elliptical shapes as we go away from it
Answer: (a) Concentric circles
Question: 3 - A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is ON. The current as seen from points A and B (in the plane of paper and on the axis of the coil) is anti clockwise and clockwise respectively. The magnetic field lines point from B to A. The N-pole of the resultant magnet is on the face close to
- A
- B
- A if the current is small, and B if the current is large
- B if the current is small and A if the current is large
Answer: (a) A
Question 4: 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
- The field lines inside the solenoid are in the form of straight lines which indicates that the magnetic field is the same at all points inside the solenoid
- The strong magnetic field produced inside the solenoid can be used to magnetise a piece of magnetic material like soft iron, when placed inside the coil
- The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet
- The N- and S-poles exchange position when the direction of current through the solenoid is reversed
Answer: (c) The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet
Question: 5 :- Commercial electric motors do not use
- An electromagnet to rotate the armature
- Effectively large number of turns of conducting wire in the current carrying coil
- A permanent magnet to rotate the armature
- A soft iron core on which the coil is wound
Answer: (c) A permanent magnet to rotate the armature
Question: 6 :- A uniform magnetic field exists in the plane of paper pointing from left to right as shown in given figure. In the field an electron and a proton move as shown. The electron and the proton experience
- Forces both pointing into the plane of paper
- Forces both pointing out of the plane of paper
- Forces pointing into the plane of paper and out of the plane of paper, respectively
- Force pointing opposite and along the direction of the uniform magnetic field respectively
Answer: (c) Forces pointing into the plane of paper and out of the plane of paper, respectively
Question: 7 :- In the arrangement shown in given figure, there are two coils wound on a non-conducting cylindrical rod. Initially the key is not inserted. Then the key is inserted and later removed. Then
- The deflection in the galvanometer remains zero throughout
- There is a momentary deflection in the galvanometer but it dies out shortly and there is no effect when the key is removed
- There are momentary galvanometer deflections that die out shortly; the deflections are in the same direction
- There are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions
Answer: (c) There are momentary galvanometer deflections that die out shortly; the deflections are in the same direction
Question: 8- Choose the incorrect statement
- Fleming’s right-hand rule is a simple rule to know the direction of induced current
- The right-hand thumb rule is used to find the direction of magnetic fields due to current carrying conductors
- The difference between the direct and alternating currents is that the direct current always flows in one direction, whereas the alternating current reverses its direction periodically
- In India, the AC changes direction after every 1/50 second
Answer: (d) In India, the AC changes direction after every 1/50 second
Question: 9 - A constant current flows in a horizontal wire in the plane of the paper from east to west as shown in Figure 13.5. The direction of magnetic field at a point will be North to South
- Directly above the wire
- Directly below the wire
- At a point located in the plane of the paper, on the north side of the wire
- At a point located in the plane of the paper, on the south side of the wire
Answer: (a) Directly above the wire
Question: 10- The strength of magnetic field inside a long current carrying straight solenoid is
- More at the ends than at the centre
- Minimum in the middle
- Same at all points
- Found to increase from one end to the other
Answer: (c) Same at all points
Question: 11 - To convert an AC generator into DC generator
- Split-ring type commutator must be used
- Slip rings and brushes must be used
- A stronger magnetic field has to be used
- A rectangular wire loop has to be used
Answer: (a) Split ring type commutator must be used
Question: 12- The most important safety method used for protecting home appliances from short circuiting or overloading is
- Earthing
- Use of fuse
- Use of stabilizers
- Use of electric meter
Answer: (b) Use of fuse