Class X – Magnetic Effects of Current (PYQs) – Solutions

Ans. No two magnetic field lines intersect each other because if they did, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible.

Ans. A₁ represents North pole and B₁ represents South pole.

Ans. It is from South pole to North pole.

Ans. Magnetic field lines are closed curves.

Ans. The magnetic lines of force do not intersect with each another due to the fact that resultant force on the north pole at any point can only be in one direction. But if the two magnetic lines of force intersect one another, then the resultant force on the north pole placed at the point of intersection will be along two directions, which is not possible.

Ans.

Ans. Soft iron core.

Ans. 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.

Ans. (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’.

Ans. Observation: The compass needle is deflected more.

Reason: Current carrying wire produces magnetic field, (B ∝ I).

Ans. Observation: The deflection of magnetic needle decreases.

Reason: The strength of magnetic field decreases with increase in distance from the wire. B ∝ 1/d

Ans. 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.

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

Ans. 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.

Ans. The closeness of lines measures the relative strength of magnetic field.

Ans. The strength of magnetic field is highest near the poles whereas minimum in the middle of bar magnet.

Ans. (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.

Ans. Soft Iron

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

Ans. Direction is out of the page

Ans. When the current in the conductor flows perpendicular (90°) to the direction of the magnetic field, maximum force is generated.

Ans. The magnetic field is in the form of parallel lines. It indicates a uniform magnetic field because magnetic field lines are parallel.

Ans. It is used to magnetise a soft iron bar to form an electromagnet.

Ans. The thumb indicates the direction of current in the straight conductor held by curved fingers of our hand.

Ans. The magnetic compass needle will get deflected near the wire current carrying but not near the wire with no current.

Ans. 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.

Ans. On observing the field lines, it shows that magnetic field due to the current carrying circular loop is maximum and normal to the current carrying loop at its centre because magnetic field due to each part of loop adds up.

(i) No two magnetic field lines intersect with each other at any point.

(ii) More crowded field lines mean a stronger magnetic field.

Ans. The movement of electrons takes place in the conductor in a particular direction when current is passed through it. These charged particles are moving in the magnetic field which experiences force. The current carrying conductor has its own magnetic field, when it superimposes the magnetic field of magnet. Due to this, current carrying conductor experiences a force. Thus conductor experiences a force when placed in a uniform magnetic field.

Factors on which direction of force depends:

(i) The direction of force depends upon the direction of magnetic field.

(ii) It also depends upon the direction of current flowing through the conductor.

26. State two ways by which the strength of an electromagnet is increased

Ans. (i) Increase in number of turns in the solenoid.

(ii) Increase in the strength of current flowing in the solenoid.

Ans. The force will act in upward direction given by thumb, if forefinger points in the direction of magnetic field and the middle finger points in the direction of current, according to Fleming’s left hand rule.

Ans. It is because current carrying conductor produces a magnetic field which superimposes with magnetic field of compass needle due to which needle of compass gets deflected.

Ans. The deflection in the magnetic needle will increase as the strength of current increases.

Ans. (a) These magnetic field lines are produced by a current carrying loop.

(b) These are magnetic field lines produced by solenoid.

Ans. 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.

Ans. A current carrying solenoid behaves like a bar magnet. When it is suspended freely it will stay in north–south direction. On reversing the direction current, it will turn to 180° because its polarity will be reversed.

Ans. The direction of motion of particles is from west to east. Fleming’s left hand rule is used to find the direction of force.

Ans. 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.

Ans. Bring one bar close to the other two one by one: if the bar attracts one of these and does not attract the other one, the bar which is not attracted is made of non-magnetic material and the bar in our hand is a magnet or a bar of magnetic material. Keep one bar on the table and move other bar along its length from one end to the other, if uniform attraction is felt the bar in our hand is a magnet and vice versa.

Ans. (i) Take a rectangular cardboard having two holes.

(ii) Insert a circular coil through these holes, normal to the plane of paper.

(iii) Connect the ends of coil in series with a battery, and key.

(iv) Sprinkle iron filings uniformly on the cardboard.

(v) Plug the key.

(vi) Tap the cardboard gently a few times. Note the pattern of the iron filings.

(vii) The pattern of magnetic field lines will be same as the pattern of iron filings.

Ans. The long coil containing large number of close turns of insulated copper wires wrapped around, is called a solenoid.

Current carrying solenoid behaves like a bar magnet. It is called an electromagnet.

It is used for making electromagnets.

Ans. (i) Take an aluminium rod, AB of size 3 inches.

(ii) Suspend it horizontally using connecting wires

(iii) Place a horse-shoe magnet in such a way that the rod lies between the two poles with magnetic field directed upwards.

(iv) Put north pole of the magnet vertically below and south pole vertically above the rod.

(v) Connect aluminium rod in series with the battery and key.

(vi) Now pass the current in the rod from B to A.

(vii) Aluminium rod will be displaced towards the left.

(viii) Now bring a stronger horse-shoe magnet and observe the displacement of rod.

(ix) The displacement of rod will increase with the increase in strength of the magnetic field.

Ans. The strength of magnetic field will increase. (B ∝ I)

Ans. The direction of magnetic field will be reversed.

Ans. The magnetic field produced will increase because magnetic field produced is directly proportional to the number of turns in the coil.

Ans. (i) direction of current, (ii) direction of magnetic field.

Ans. When direction of current is perpendicular to the direction of magnetic field, the force experienced will be maximum.

Ans. No, force is exerted by a proton beam because proton beam is moving along the direction of magnetic field.

41. How can a solenoid be utilised to make an electromagnet?

Ans. By inserting a soft iron rod into the middle part of solenoid it is used to make an electromagnet

Ans. The force experienced by a current carrying conductor when placed in a magnetic field or the force experienced by a charged particles moving in a magnetic field is called magnetic force.

Fleming left hand rule: According to this rule, on stretching the thumb, forefinger and the middle finger of your left hand such that these are perpendicular to each other, if the force finger points in the direction of magnetic field and middle finger in the direction of current, then the thumb will point in the direction of motion of force acting on the conductor.

(i) If magnitude of current is doubled, then force is doubled.

(ii) If direction of flow of current is reversed, the direction of force is also reversed.

(iii) If direction of magnetic field is reversed, the direction of force is also reversed.

Ans. It may be greater than or less than primary coil.

Ans. It can be done by moving a magnet towards the coil.

Ans. There are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions

Ans. (a) It will show deflection.

(b) The deflection will be in the opposite direction.

(c) The galvanometer will not show any deflection.

Ans. (i) Direct current should be used.

(ii) Magnitude of current should be large.

(iii) The number of turns in solenoid are more and close to each other like windings in an electric motor.

(iv) The soft core inside the solenoid should be made up of steel.

Ans. It is the phenomena of production of induced current and potential difference in a conductor by moving a magnet or if there is a change in magnetic field or flux.

Fleming’s right hand rule for determining the direction of induced current: Hold the thumb, the forefinger and central finger of your right hand perpendicular to each other in such a way that forefinger represents the direction of magnetic field, the thumb points in the direction of motion of conductor, then the central finger will give the direction of induced current in the conductor.

Ans. • Either the coil or the magnet should be in motion

• If there is relative motion between a coil carrying current and coil not carrying current, there will be induced current in the second coil.

• No current will be induced because there is no change in magnetic field which is essential to produce induced current.

Ans. • Take a coil of wire AB having a large number of turns.

• Connect the ends of the coil to a galvanometer as shown in figure.

• Take a strong bar magnet and move its north pole towards the end B of the coil.

• There is a momentary deflection in the needle of the galvanometer, say to the right. This indicates the presence of a current in the coil AB. The deflection becomes zero the moment the motion of the magnet stops.

• Now withdraw the north pole of the magnet away from the coil. Now the galvanometer is deflected toward the left, showing that the current is now set up in the direction opposite to the first.

Fleming’s right hand rule is used find the direction of electric current generated in the coil.

Ans. The galvanometer needle deflects momentary in one direction because when the key is closed, magnetic field lines around coil-2 increases momentarily that causes induced current in coil-2.

Ans. The galvanometer needle deflects momentarily but in opposite direction because when the key is opened, magnetic field lines around coil-2 decreases momentarily that causes induced current in coil-2