CBSE Class 10 Physics Magnetic Effect of Electric Current Worksheet Set B

Question. At what place of the magnet are the magnetic field lines closer ?
Answer: Near the poles of the magnet.

Question. State Ampere’s swimming rule.
Answer: If a swimmer swims in the direction of current, facing the magnetic needle, then the north pole of the magnetic needle deflects towards his left hand i.e., west and the south pole towards his right hand i.e., east.

Question. Why does a current carrying freely suspended solenoid rest along a particular direction ? State the direction in which it rests.
Answer: A current carrying solenoid behaves like a bar magnet. It rest in geographic north-south direction.

Question. What is the role of a split ring in an electric motor? 
Answer: In an electric motor, after every half rotation the direction of coil gets reversed due to change in orientation of the magnetic field. To ensure a continuous rotation; a split ring is attached to the coil so that the polarity of the coil changes after every half rotation. This changes the direction of current and thus the armature keeps on rotating continuously.

Question. How is the strength of the magnetic field at a point near a wire related to the strength of the electric current flowing in the wire ?
Answer: Strength of magnetic field is directly proportional to the strength of current flowing in the wire.

Question. State the observation made by Oersted on the basis of his experiment with current-carrying conductors ?
Answer: Every current-carrying conductor has a magnetic field around it.

Short Answer Type Questions :

Question. Answer the following question:
(a) What type of magnetic field is produced due to a straight current carrying conductor?
(b) The magnetic field lines produced by a straight solenoid resemble the magnetic field lines produced by another object.
Identify that object.
Answer: (a) Magnetic field lines are concentric circular loops in a plane perpendicular to the straight conductor. The centres of the circular lines lie on the conductor.
(b) The magnetic field produced due to a straight solenoid is similar to that produced by a bar magnet.

Question. Answer the following questions:
(a) State Ampere’s swimming rule.
(b) Name and state the rule to determine the direction of magnetic field produced by a straight wire carrying current.
Answer: (a) If a swimmer swims in the direction of current, facing the magnetic needle, then the north pole of the magnetic needle deflects towards his left hand i.e., west and the south pole towards his right hand i.e., east.
(b) Maxwell’s right hand thumb rule is used to determine the direction. According to this rule, when you hold a current carrying conductor in your right hand in such a way that your
thumb points in the direction of the current then the direction in which your fingers encircle the conductor will give the direction of magnetic field around it.

Question. State the direction of magnetic field in the following diagram. 

Answer: As per Fleming's left hand rule, the magnetic field is directed out of the paper. 

Question. A wire is placed between N and S poles of a magnet as shown in figure. If current flows in the wire as shown, in which direction does the wire tend to move? 

Answer: The direction of magnetic field is from N-pole to S-pole; on applying Fleming's left-hand rule, the wire tends to move perpendicular to plane of paper upward. 

Question. The given magnet is divided into three parts A, B and C as:
                          A         B           C
Name the part when the strength of magnetic field is (i) maximum, (ii) minimum. How will the density of magnetic field lines differ at these parts?
Answer: (i) Maximum of magnetic field strength is at ‘A’ and ‘C’
(ii) Minimum of magnetic field strength is at ‘B’.
At ‘A’ and ‘C’ magnetic field lines are crowded whereas these are spread out at ‘B’.

Question. (a) Two magnets are lying side by side as shown below. Draw magnetic field lines between the poles P and Q

(b) What does the degree of closeness of magnetic field lines near the poles signify?

Answer: (a) Magnetic field lines are shown below

(b) It shows that magnetic field is stronger near the poles, i.e. the pole of another magnet when placed in the magnetic field of a magnet will experience greater force. That is why field lines are crowded

Question. Given below are three diagrams showing entry of an electron in a magnetic field. Identify the case in which the force on electron will be maximum and minimum respectively. Give reason for your answer. Find the direction of maximum force acting on electron. 

Answer: Force on electron is maximum in fig. (a) because here direction of motion of electron is at right angles to that of magnetic field ‘B’. The force is minimum (or zero) in fig. (c) because here electron is moving along the direction of magnetic field B. The direction of maximum force acting on electron is perpendicular to the plane of paper and directed into it.

Question. AB is a current carrying conductor in the plane of the paper as shown in figure. What are the directions of magnetic fields produced by it at points P and Q ? Given r1 > r2, where will the strength of the magnetic field be larger? 
Answer: Since the direction of the current in the current carrying conductor AB is upwards, the direction of the magnetic field would be anti-clockwise as deduced by applying right hand thumb rule. Consequently, the magnetic field at point P would be towards the plane and, at point Q, the direction of the magnetic field would be away from the plane.
Since the strength of the magnetic field is inversely proportional to the distance (r), the field at P would be weaker as compared to Q [·.· r1 > r2].

Question. Magnetic field lines of two magnets are shown in figure A and figure B.

Select the figure that represents the correct pattern of field lines. Give reasons for your answer. Also name the poles of the magnets facing each other.
Answer: Figure ‘B’ represents correct pattern of magnetic field lines because magnetic field lines never intersect each other. If these intersect there will be two directions of the magnetic field at the point of intersection, which is not possible. In figure B. field lines are emerging (going away) from the magnet, so both the poles are north poles.

Question. What are magnetic field lines? Explain why magnetic field lines are closed curves?
Answer: The closed path traced by the unit North pole (imaginary) in a magnetic field are called magnetic field lines.
They are continuous closed curves because they diverge from the north pole of a bar magnet and converge to its south pole.

Question. Identify the poles of the magnet in the given figure (1) and (2).

Answer: Field lines emerge from North pole and merge at South pole (S). So, X represents North pole and Y represents South pole.

Question. The directions of current flowing in the coil of an electromagnet at its two ends X and Y are as shown in given figure.
(a) What is the polarity of end X ?
(b) What is the polarity of end Y ?
(c) Name the rule which you have used to determine the polarities. 

Answer: (a) Since current at end X is anticlockwise, the polarity at that end is North pole.
(b) Current at end Y is clockwise, hence polarity at that end is South pole.
(c) Clock-face rule is used to determine the polarities of the two faces of a current carrying circular loop.

Question. What are magnetic field lines? How is the direction of magnetic field at a point deter- mined?
Answer: (i) The magnetic field lines produced is into the plane of the paper at R and out of it at S
(ii) Field at S > Field at P
Magnetic field strength for a straight current carrying conductor is inversely proportional to the distance from the wire
(iii) The current will be going from top to bottom in the wire shown and the magnetic field lines are now in the clockwise direction on the plane which is perpendicular to the wire carrying current.
(iv) Right hand thumb rule. The thumb is aligned to the direction of the current and the direction in which the fingers are wrapped around the wire will give the direction of the magnetic field.

Question. Why does it become more difficult to move a magnet towards a coil when the number of turns in a coil have been increased?
Answer: It becomes more difficult to move a magnet towards a coil when the number of turns in the coil is increased because the induced current in the coil due to electromagnetic induction increases and the induced current opposes the motion of the magnet towards the coil.

Question. Describe an activity to determine the direction of magnetic field produced by a current carrying straight conductor. Also show that the direction if the magnetic field is reversed on reversing the direction of the current.
Answer: (i) Take a straight vertical wire AB passing through a horizontal cardboard ‘C’.
(ii) The ends of wires are connected to a battery and a switch.
(iii) When the current is passed through the wire AB, it produces a magnetic field around it, which can be shown by sprinkling iron filings on the cardboard ‘C’.
(iv) The iron filings get magnetised and arrange themselves in concentric circles around the wire.
(v) It shows that magnetic field of lines are circular in nature.
(vi) When current passed in the wire it flows in upward direction, the lines of force are in anticlockwise direction.
(vii) Now pass current from B to A, i.e. in downward direction, the magnetic lines of force will be clockwise.

Question. Draw magnetic field lines around a bar magnet.
Answer:

Question. A compass needle is placed near a current-carrying wire. State your observation for the following cases, and give reason for the same in each case.
(a) Magnitude of electric current in the wire is increased.
(b) The compass needle is displaced away from the wire.
Answer: (a) Observation: The compass needle is deflected more.
Reason: Current carrying wire produces magnetic field, (B μ I).
(b) Observation: The deflection of magnetic needle decreases.
Reason: The strength of magnetic field decreases with increase in distance from the wire.

Question. The magnetic field associated with a current carrying straight conductor is in anticlockwise 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.
Answer: When the observer observes the direction of magnetic field from west then the direction of current is from east to west and if observer is at east side then the direction of current is from west to east. Right hand thumb rule: If we hold a current carrying conductor in our right hand in a such a way that stretched thumb is along the direction of the current, then curls of fingers around the conductor represents the direction of magnetic field lines.

Question. (a) In a pattern of magnetic field lines due to bar magnet, how can the regions of relative strength be identified?
(b) Compare the strength of magnetic field near the poles and the middle of a bar magnet
Answer: (a) The closeness of lines measures the relative strength of magnetic field.
(b) The strength of magnetic field is highest near the poles whereas minimum in the middle of bar magnet.

Question. PQ is a current carrying conductor in the plane of the paper as shown in the figure below.
(i) Find the directions of the magnetic fields produced by it at points R and S?
(ii) Given r1> r2, where will the strength of the magnetic field be larger? Give reasons.
(iii) If the polarity of the battery connected to the wire is reversed, how would the direction of the magnetic field be changed?
(iv) Explain the rule that is used to find the direction of the magnetic field for a straight current carrying conductor.

Answer: (i) The Magnetic field lines produced is into the plane of the paper at R and out of it at S.
(ii) Field at S > Field at P
Magnetic field strength for a straight current carrying conductor is inversely proportional to the distance from the wire.
(iii) The current will be going from top to bottom in the wire shown and the magnetic field lines are now in the clockwise direction on the plane which is perpendicular to the wire carrying current.
(iv) Right hand thumb rule. The thumb is aligned to the direction of the current and the direction in which the fingers are wrapped around in wire will give the direction of the magnetic field.

Case Based Questions :

Read the passage carefully and answer any four questions from The magnetic field lines of an infinite wire are circular and centered at the wire and they are identical in every plane perpendicular to the wire as shown in the figure. 

Since the field decreases with distance from the wire, the spacing of the field lines must increase correspondingly with distance. The direction of this magnetic field may be found with a second form of the right-hand rule. If you hold the wire with your right hand so that your thumb points along the current, then your fingers wrap around the wire in the same sense as B→.

Question. A vertical wire carries an electric current out of the page. What is the direction of the magnetic field at point P located to the west from the wire?
(a) North
(b) South
(c) East
(d) Down

Answer: B

Question. A student writes the following statements on the characteristics of magnetic field lines: 
(I) The magnetic field lines are imaginary lines.
(II) The magnetic field lines has only magnitude.
(III) The magnetic field lines are closed curves.
(IV) The magnetic field lines emerge from the south pole of a magnet.
Choose the correct statement(s) from the following:
(a) Only (I)
(b) Both (I) and (II)
(c) Both (I) and (III)
(d) Both (II) and (IV)

Answer: C

Question. A current carrying conductor is held in exactly vertical direction. 
In order to produce a clockwise magnetic field around the conductor, the current should be passed in the conductor:
(a) from top to bottom
(b) from left to right
(c) from bottom to top
(d) from right to left

Answer: A

Question. A student plotted the variation of magnetic field around a straight current carrying wire and the distance from the wire where the magnetic field is measured. Study the graph below and answer the question that follows: 

The magnetic field around a current carrying straight wire:
(a) increases linearly with increase in distance.
(b) decreases with increase in distance.
(c) remains constant.
(d) magnetic field at a point does not depend on distance.

Answer: B

Question. A positive charge is moving towards a person. The direction of magnetic field lines will be in:
(a) clockwise direction
(b) anticlockwise direction
(c) vertically upward direction
(d) vertically downward direction

Answer: B

Read the passage carefully and answer the following questions from When a small compass is placed near a magnet, it will experience a force due to the magnetic field of the magnet. It is evidently observed due to a deflection in the north pole pointer of the compass. The path traced by the north pole pointer under the influence of a magnetic field is called the magnetic field line. The magnetic field lines are produced from the north pole of the magnet end at the south pole of the magnet. When the compass is moved around the field line, it always sets itself tangential along the curves.

Question. The magnetic field lines:
(a) intersect at right angle to one another.
(b) intersect at an angle of 45 degree.
(c) cross at an angle of 60 degree.
(d) never intersect with each other.

Answer: D

Question. Magnetic field lines can be used to determine: 
(a) the shape of the magnetic field.
(b) only the direction of the magnetic field.
(c) only the relative strength of the magnetic field.
(d) both the direction and the relative strength of the magnetic field.

Answer: D

Question. The magnetic field lines due to a bar magnet are correctly shown 

Answer: D

Question. Which of the following is incorrect regarding magnetic field lines? 
(a) The field lines are directed N to S inside the magnet.
(b) The Crowdedness of the field lines shows the strength of the magnet.
(c) The field is tangent to the magnetic field line.
(d) Magnetic field lines are closed and continuous curves.

Answer: A

Question. A strong bar magnet placed vertically above a surface. The magnetic field lines will be: 
(a) Only in a horizontal plane around the magnet.
(b) Only in a vertical plane around the magnet.
(c) Both in horizontal and vertical plane around the magnet.
(d) In all the planes around the magnet.

Answer: D

Read the passage carefully and answer the following questions from A current-carrying wire produces a magnetic field around it. The phenomena in which an electromotive force and current are induced by changing magnetic field through it is called induced current. It can be concluded that the induced current flows in a conductor as long as the magnetic force changes within the conductor. For the motion of the coil with respect to the magnet or vice versa, the direction of the current flowing in the conductor is determined by the direction of the relative motion of the conductor with respect to the magnetic field. The induced emf or current is directly proportional to the rate of change in the magnetic field. 

Question. What is the condition of electromagnetic induction?
(a) There must be relative motion between galvanometer and coil of wire.
(b) There must be a relative motion between galvanometer and magnet.
(c) There must be a relative motion between galvanometer and electric motor.
(d) There must be a relative motion between the coil of wire and a magnet.

Answer: D

Question. An induced emf is produced when a magnet is plugged into a coil. The magnitude of induced emf does not depend upon:
(a) The number of turns in the coil.
(b) The speed with which the magnet is moved.
(c) The resistivity of the material of the coil.
(d) The strength of the magnet.

Answer: C

Question. A bar magnet is pushed steadily into a long solenoid connected to a meter. 
Which of the following would affect the magnitude of the deflection of the meter?
(a) How fast the magnet is pushed into the coil.
(b) Direction in which the coil is wound.
(c) End of the solenoid where the magnet enters.
(d) Pole of the magnet which enters the coil first.

Answer: A

Question. A conducting rod moves across two magnets as shown in the figure and the needle in the galvanometer deflects momentarily. 
This physical phenomenon is called:
(a) Induced magnetism
(b) Electromagnetism
(c) Static induction
(d) Electromagnetic induction

Answer: D

Question. Magnetic lines of force inside current-carrying solenoid are:
(a) perpendicular to axis.
(b) along the axis and are parallel to each other.
(c) parallel inside the solenoid and circular at the ends.
(d) circular.

Answer: B