AP 10th Class Physics 12th Lesson Questions and Answers Magnetic Effects of Electric Current

AP State Board new syllabus AP Board Solutions Class 10 Physics 12th Lesson Magnetic Effects of Electric Current Questions and Answers.

10th Class Physics 12th Lesson Magnetic Effects of Electric Current Questions and Answers

10th Class Physics 12th Lesson Questions and Answers (Exercise)

Question 1.
Which of the following correctly describes the magnetic field near a long straight 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 centred on the wire.
Answer:
d) The field consists of concentric circles centred on the wire.

Question 2.
At the time of short circuit, the current in the circuit
a) reduces substantially.
b) does not change,
c) increases heavily.
d) vary continuously.
Answer:
c) increases heavily.

Question 3.
State whether the following statements are true or false.
a) The field at the centre of a long circular coil carrying current will be parallel straight lines.
b) A wire with a green insulation is usually the live wire of an electric supply.
Answer:
a) True : The field is almost uniform at the centre of the coil.
b) False : The wire with green insulation is usually the live wire.

Question 4.
List two methods of producing magnetic fields.
Answer:
Permanent magnets, electromagnets and earth’s magnetic field.

Question 5.
When is the force experienced by a current-carrying conductor placed in a magnetic field largest ?
Answer:
When the conductor carries current in a direction perpendicular to the direction of the magnetic field, the force experienced by the conductor is largest.

Question 6.
Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field ?
Answer:
According to Fleming’s left hand rule, the magnetic field acts in the vertically downward direction. Note that the direction of current will be opposite to that of the electron beam.

Question 7.
State the rule to determine the direction of a
i) magnetic field produced around a straight conductor-carrying current,
ii) force experienced by a current-carrying straight inductor plated in a magnetic field which is perpendicular to it, and
iii) current induced in a coil due to its rotation in a magnetic field.
Answer:
i) Right hand thumb rule : If the current carrying conductor is held in the right hand such that the thumb points in the direction of the current, then the direction of the curl of the fingers will give the direction of the magnetic field.

ii) Fleming’s left hand rule : Stretch the forefinger, the central finger and the thumb of . the left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field, the central finger in the direction of current, then the thumb points in the direction of force in the conductor.

iii) Fleming’s right hand rule : Stretch the thumb, forefinger and the central finger of the right hand mutually perpendicular to each other. If the forefinger points in the 1 directions of magnetic field, thumb in the direction of motion of the conductor, then the central finger points in the direction of current induced in the conductor.

Question 8.
When does an electric short circuit occur ?
Answer:
As a result of live wire touching the neutral wire, the resistance offered to the flow of current becomes almost zero and this is called short-circuiting. In this situation, a large current flows through the circuit, causes a spark or damage to the appliance.

Question 9.
What is the function of an earth wire? Why is it necessary to earth metallic appliances ?
Answer:
The earth wire connects the metallic body of the high powered appliance to the earth. It is a safety measure which ensures any leakage of current of the metallic body of the appliance keeps its potential equal to that of the earth (zero volt) and the user may not get a severe electric shock.

10th Class PS 12th Lesson Questions and Answers (InText)

Page No. 284

Question 1.
Why does a compass needle get deflected when brought near a bar magnet ?
Answer:
The magnetic field of the magnet exerts force on both the poles of the compass needle. The forces experienced by the two poles are equal and opposite. These two forces from a couple which deflects the compass needle.

Page No. 292

Question 2.
Draw magnetic field lines around a bar magnet.
Answer:

Question 3.
List the properties of magnetic field lines.
Answer:

1. These are closed curves which start from N-pole and end at the S-pole and then return to the N-pole through the interior of the magnet.
2. No two magnetic lines of force can intersect each other.
3. They start from and end on the surface of the magnet normally.
4. The lines of force have a tendency to contract lengthwise and expand sidewise. This explains attraction between unlike poles and repulsion between like poles.
5. The relative closeness of the lines of force gives a measure of the strength of the magnetic field which is maximum at the poles.

Question 4.
Why don’t two magnetic field lines intersect each other ?
Answer:
The two magnetic field lines do not intersect each other. If they intersect at the point of intersection, then there will be two different.directions of magnetic field, which is impossible.

Page No. 294

Question 5.
Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.
Answer:

Since the current passes through the loop in clockwise direction, therefore, the front face of the loop will be the south pole and the back face, i.e., the face touching the table will be north pole.
According to right-hand rule, the direction of the magnetic field will be upward.

Question 6.
The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer:
A uniform magnetic field in a region is represented by drawing parallel and equidistant straight lines, all pointing in the same direction.

Page No. 296

Question 7.
Choose the correct option. The magnetic field inside a long straight solenoid-carrying current
a) is zero.
b) decreases as we move towards its ends.
c) increases as we move towards its ends.
d) is the same at all points.
Answer:
The field lines inside the solenoid are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid. Thus, option (d) is correct.

Page No. 298

Question 8.
Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)
(a) mass
(b) speed
(c) velocity
(d) momentum
Answer:
When a proton moves freely in a magnetic field, the following properties can„change :
b) Speed : The speed of a proton can change as it is affected by the magnetic field, causing it to accelerate or decelerate.

d) Momentum : Momentum is directly related to an object’s mass and velocity. As the proton’s speed and/or direction (velocity) change in the magnetic field, its momentum will also change.

c) Velocity : The direction and magnitude of the proton’s velocity can change as it is deflected by the magnetic field, so its velocity can change.
So, the correct answers are (b) speed, (d) momentum, and (c) velocity.

Question 9.
In Activity 12.7, how do we think the displacement of rod AB will be affected if (i) current in rod AB is increased; (ii) a stronger horse-shoe magnet is used; iii) length of the rod AB is increased .
Answer:

1. When the current in the rod AB is increased, force exerted on the conductor increases, so the displacement of the rod increases.
2. When a stronger horse shoe magnet is used, the magnitude of the magnetic field increases. This increases the force exerted on the rod and the displacement of the rod.
3. The displacement of the rod will increase, because F ∝ L.

Question 10.
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:
c) downward
Explanation :

1. The direction of the magnetic field is downward.
2. This is because a positively charged particle (alpha-particle) moving towards the west is deflected towards the north by a magnetic field according to the right-hand rule.
3. Therefore, the magnetic field must be directed downward.

Page No. 302

Question 11.
Name two safety measures commonly used in electric circuits and appliances.
Answer:

1. Earthing and
2. Electric fuse.

Question 12.
An electric oven of 2 kW power rating is operated in a domestic eleetric circuit (220 V) that has a current rating of 5 A. What result do you expect ? Explain.
Answer:
The electric oven draws a current given by I = \(\frac{P}{V}\) = \(\frac{2 \mathrm{KW}}{220 \mathrm{~V}}\) = \(\frac{2000 \mathrm{~W}}{220 \mathrm{~V}}\) = 9.09A.
Thus the electric oven draws current much more than the current rating of 5A. That is, the circuit is overloaded. Due to exessive current, the fuse wire blows and the circuit is broken.

Question 13.
What precaution should be taken to avoid the overloading of domestic electric circuits ?
Answer:
As a result of overloading, the connecting wires get over-heated and the appliances may get damaged. To avoid this, the following safety measures must be taken.

1. The wires used in the circuit must be coated with good insulating materials like PVC, etc.
2. The circuit must be divided into different sections and a safety fuse must be used in each section.
3. High power appliances like air-conditioner, refrigerator, water heater, etc., should not be used simultaneously.

Example Problems [Textbook]

Question 1.
A current through a horizontal power line flows in east to west direction. What is
the direction of magnetic field at a point directly below it and at a point directly above it ? (T.B. Page No. 290)
Solution:
The current is in the east-west direction. Applying the right-hand thumb rule, we get that the magnetic field (at any point below or above the wire) turns clockwise in a plane perpendicular to the wire, when viewed from the east end, and anti-clockwise, when viewed from the west end.

Question 2.
An electron enters a magnetic field at right angles to it,
as shown in Figure. The direction of force acting on the electron will be (a) to the right, (b) to the left.
(c) out of the page, (d) into the page. (T.B. Page No. 298)

Solution:
Answer is option (d) Electron
The direction of force is perpendicular to the direction of magnetic field and current as given by Fleming’s left hand rule. Recall that the direction of current is taken opposite to the direction of motion of electrons. The force is therefore directed into the page.

AP 10th Class Physical Science Chapter 12 Questions and Answers (Lab Activities)

Activity – 12.1 (Page. No. 282)

Question 1.
Prove that electricity and magnetism are linked to each other.
(OR)
Prove that the electric current through the copper wire has produced a magnetic effect.
Answer:
Aim : To demonstrate that a magnetic field is produced around a current carrying wire.
Apparatus required : A thick copper wire, a compass needle, a plug-key, a resistance wire, a battery, of 6V and connecting wires.
Procedure :

1. Take a straight thick copper wire, along straight conductor and place it between the points X and Y in an electric D circuit, as shown in Figure.
2. Horizontally place a small compass near to this copper wire. See the position of its needle.
3. Pass the current through the circuit by inserting the key into the plug.
4. Observe the change in the position of the compass needle.

Observation and Conclusion : As we pass current through the copper wire XY, the compass needle gets deflected from its position of rest. Since a magnetic needle can be deflected only by a magnetic fieid. So the current carrying wire produces a magnetic field around it or it behaves like a magnet.

Activity – 12.2 (Page. No. 284)

Question 2.
Write an activity to demonstrate magnetic field lines around a magnet.
Answer:
Aim : To study the pattern of the field lines of a bar magnet by using iron fillings.
Apparatus required : Bar magnet, sheet of white paper, iron filings.
Procedure :

1. Fix a sheet of white paper on a drawing board using some adhesive material.
2. Place a bar magnet in the centre of it.
3. Sprinkle some iron filings uniformly around the bar magnet (Figure). A salt-sprinkler may be used for this purpose.
4. Now tap the board gently.

Observations :

1. The iron filings arrange themselves in a pattern as shown in Figure.
2. The magnet exerts a force on the iron filings of the surrounding region.
3. This force arranges the iron filings along definite lines extending from one end of the magnet to the other.

Conclusion :

1. The region surrounding a magnet, in which the force of the magnet can be detected, is said to have a magnetic field.
2. The lines along which the iron filings align themselves represent magnetic field lines.

Activity – 12.3 (Page. No. 284)

Question 3.
How do you draw the field lines around a bar magnet ?
Answer:
Aim : To plot of a complete pattern of the field lines of bar magnet with the help of a compass needle.
Apparatus required : A sheet of white paper, a drawing board, adhesive tape, a bar magnet, a compass needle and a pencil.
Procedure :

• Take a small compass and a bar magnet.
• Place the magnet on a sheet of white paper fixed on a drawing board, using some adhesive material.
• Mark the boundary of the magnet.
• Place the compass near the north pole of the magnet. How does it behave ? The south pole of the needle points towards the north pole of the magnet. The north pole of the compass is directed away from the north pole of the magnet.
• Mark the position of two ends of the needle.
• Now move the needle to a new position such that its south pole occupies the position previously occupied by its north pole.
• In this way, proceed step by step till you reach the south pole of the magnet as shown in fig. (a).

• Join the points marked on the paper by a smooth curve. This curve represents a field line.
• Repeat the abdve procedure and draw as many lines as you can. You will get a pattern shown in fig. (b) These lines represent the magnetic field around the magnet. These are known as magnetic field lines.
• Observe the deflection in the compass needle as you move it along a field line. The deflection increases as the needle is moved towards the poles.

Observations :

1. The deflection of the compass needle increases as it is moved towards the poles.
2. This is because the magnetic field is stronger near the two poles and hence exerts larger force on the compass needle in such regions.

Conclusion :

1. Magnetic field is a quantity that has both direction and magnitude.
2. The direction of the magnetic field is taken to be the direction in which a north pole of the compass needle moves inside it.
3. Therefore it is taken by convention that the field lines emerge from north pole and merge at the south pole (note the arrows marked on the field lines in fig.)
4. Inside the magnet the direction of field lines is from its south pole to its north pole. Thus the magnetic field lines are closed curves.

Activity – 12.4 (Page. No. 286)

Question 4.
Write an activity to demonstrate the direction of the field produced around a current-carrying conductor.
Answer:
Aim : To study the dependence of the magnetic field on the direction of current through the conductor.
Apparatus required : Long straight copper wire, two or three cells of 1.5 V each, plug key and compass needle.
Procedure:

• Take a long straight copper wire, two or three cells of 1.5 V each, and a plug key. Connect all of them in series as shown in Fig.(a).
• Place the straight wire parallel to and over a compass needle.
• Plug the key in the circuit.
• Observe the direction of deflection of the north pole of the needle. If the current
  flows from north to south, as shown in fig. (a), the north pole of the compass needle would move towards the east.

1. Replace the cell connections in the circuit as shown in fig.(b). This would result in the change of the direction of current through the copper wire, that is, from south to north.
2. Observe the change in the direction of deflection of the needle. You will see that now the needle moves in the opposite direction, that is, towards the west [fig. (b)].

Observation : When we reverse the direction of current in the conductor, the direction of the compass needle is also reversed.

Conclusions :

1. This shows that the direction of the magnetic field produced by the electric current has also reversed.
2. Thus the direction of magnetic field produced by a current carrying conductor depends on the direction of current through it.

Activity – 12.5 (Page. No. 288)

Question 5.
Write an activity to demonstrate the shape and direction of the magnetic field lines around a current-carrying wire.
Answer:
Aim: To study the pattern of the magnetic field lines around a straight current carrying
conductor.
Apparatus required : Battery (12 V), rheostat, ammeter (0 – 5 A), a plug key, connecting wires, a long straight thick copper wire, and cardboard.

Procedure :

1. Take a battery (12 V), a variable resistance (or a rheostat), an ammeter (0 – 5 A), a
   plug key, connecting wires and a long straight thick copper wire.
2. Insert the thick wire through the centre, normal to the plane of a rectangular card¬board. Take care that the cardboard is fixed and does not slide up or down.
3. Connect the copper wire vertically between the points X and Y, as shown in Fig. (a), in series with the battery, a plug and key.
4. Sprinkle some iron filings uniformly on the cardboard. (You may use a salt sprinkler for this purpose.)
5. Keep the variable of the rheostat at a fixed position and note the current through the ammeter.
6. Close the key so that a current flows through the wire. Ensure that the copper wire placed between the points X and Y remains vertically straight.
7. Gently tap the cardboard a few times. Observe the pattern of the iron filings. You would find that the iron filings align themselves showing a pattern of concentric circles around the copper wire (fig).
8. They represent the magnetic field lines.
9. Place a compass at a point (say P) over a circle. Observe the direction of the needle. The direction of the north pole of the compass needle would give the direction of the field lines produced by the electric current through the straight wire at point P. Show the direction by.
10. Does the direction of magnetic field lines get reversed if the direction of current through the straight copper wire is reversed ?

Observation and Conclusions :

1. When the direction of current through the straight wire is reversed, the direction of magnetic field lines also gets reversed as can be seen by the deflection in the compass needle. „
2. The concentric circles representing the field lines around a current carrying straight wire become larger and larger we move away from the wire.

Activity – 12.6 (Page. No. 292)

Question 6.
Write an activity to demonstrate magnetic field lines around a current-carrying loop and describe the magnetic field lines formed.
Answer:
Aim : To study the pattern of the magnetic field lines produced by a current – carrying circular coil.
Apparatus required : A rectangular cardboard having two holes, a circular coil having a large number of turns, a battery, a rheostat, a plug-key, connecting wires, iron filings and a compass needle.
Procedure :

1. Take a rectangular cardboard having two holes. Insert a circular coil having large number of turns through them, normal to the plane of the cardboard.
2. Connect the ends of the coil in series with a battery, a key and a rheostat, as shown in Figure.
3. Sprinkle iron filings uniformly on the cardboard.
4. Plug the key.
5. Tap the cardboard gently a few times. Note the pattern of the iron filings that emerges on the cardboard.

Observation and Conclusion : We obtain a pattern of the magnetic field lines as shown in figure, clearly, the lines of force are almost concentric circles near the wire. At the centre of the loop, the lines of force are almost parallel straight lines. Thus the magnetic field is uniform near the centre of the loop.

Activity – 12.7 (Page. No. 296)

Question 7.
Write an activity to prove that a force is exerted on the current-carrying aluminium rod when it is placed in a magnetic field.
(OR)
Write an activity to prove that the direction of force is also reversed when the direction of current through the conductor is reversed.
Answer:
Aim : To demonstrate the existence of force on current carrying conductor in a magnetic field.
Apparatus required : A small aluminium rod of about 5 cm length, a strong horse shoe magnet, a battery, a plug-key, a vertical stand and connecting wires.

Procedure :

1. Take a small aluminium rod AB (of about 5 cm). Using two connecting wires suspend it horizontally from a stand, as shown in Figure.
2. Place a strong horse-shoe magnet in such a way that the rod lies between the two poles with the magnetic field directed upwards. For this put the north pole of the magnet vertically below and the south pole vertically above the aluminium rod (figure).
3. Connect the aluminium rod in series with a battery, a key and a rheostat.
4. Now pass a current through the aluminium rod from end B to end A.
5. What do you observe? It is observed that the rod is displaced towards the left. You will notice that the rod gets displaced.
6. Reverse the direction of current flowing through the rod and observe the direction of its displacement. It is now towards the right ?
7. Why does the rod get displaced?

Observation and Conclusion :

1. The aluminium rod gets displaced because a force is exerted on the current – carrying rod when it is placed in a magnetic field.
2. When the direction of current in the rod is reversed, the direction of displacement of rod or the direction of force on the rod is also reversed.
3. The displacement of the rod is largest or the magnitude of the force is-maximum when the direction of current is perpendicular to the direction of the magnetic field.