You will learn more about the connection between electricity and magnetism and examine the various ways that electric current can create a magnetic field in Chapter 13 of Class 10 Science (NCERT, NBSE, SEBA, TBSE etc.), “Magnetic Effects of Electrical Current.” You will gain knowledge of Hans Christian Oersted and Michael Faraday’s groundbreaking research, two scientists who laid the groundwork for our knowledge of electromagnetism and its numerous practical applications. You will also learn about the heating effects of electric current, how current-carrying wires behave as magnets, Fleming’s left-hand rule, and the fundamentals of electric motors. Get here the questions, answers, textbook solutions, PDF, MCQs of this chapter.
Intext / page 235
1. Why does a compass needle get deflected when brought near a bar magnet?
Answer: The magnetic field exists around both a bar magnet and a magnetic compass needle. When they are brought close to one another, these magnetic fields interact, deflecting the needle.
Intext / page 239
1. Draw magnetic field lines around a bar magnet.
Answer:
2. List the properties of magnetic lines of force.
Answer: The following describes the characteristics of magnetic lines of force, also referred to as magnetic field lines: The magnetic field lines outside the magnet are pointed in the direction of the magnet’s S-pole from its N-pole. The field lines, however, in a magnet are pointed from S-pole to N-pole. Thus, magnetic field lines form a close loop. Any point’s magnetic field line points in the direction of the magnetic field there. The degree of closeness of the field lines determines the relative strength of magnetic fields. Where the field lines are densely packed, there is a strong magnetic field. It is impossible for two magnetic field lines to ever intersect.
3. Why don’t two magnetic lines of force intersect each other?
Answer: It is discovered that no two field lines cross one another. If they did, the compass needle at the intersection would point in two different directions, which is not possible.
Intext / page 240-41
1. 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: The figure below displays the magnetic field lines. According to the right-hand rule, we discover that the magnetic field lines are pointed inward and perpendicular to the plane of the paper inside the loop. Outside the loop, magnetic field lines are pointed away from the paper’s surface.
2. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer: The uniform magnetic field is represented by parallel, equidistant lines of equal length as shown in Figure.
3. Choose the correct option. The magnetic field inside a long straight solenoid-carrying current (a) is zero. (b) decreases as we move towards its end. (c) increases as we move towards its end. (d) is the same at all points.
Answer: (d) is the same at all points.
Intext / page 242-243
1. 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: (c) Velocity and (d) Momentum
2. In Activity 13.7, 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; and
(iii) length of the rod AB is increased?
Answer: (i) Increasing the current in rod AB will result in an increase in displacement.
(ii) The displacement of rod AB will rise if we use a stronger horse-shoe magnet.
(iii) As the rod’s length increases, the force acting on it does as well, causing the rod’s displacement to rise.
3. A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
Answer: (d) upward In accordance with Fleming’s left-hand rule, the direction of magnetic field is vertically upward.
Intext / page 242-244
1. State Fleming’s left-hand rule.
Answer: Stretch your left hand’s thumb, forefinger, and middle finger until they are perpendicular to one another, as per Fleming’s left-hand rule. The thumb will point in the direction of motion or the force acting on the conductor if the first finger points in the direction of the magnetic field and the second finger points in the direction of current.
2. What is the principle of an electric motor?
Answer: An electric motor’s operation is based on the magnetic pull of current. When positioned in a magnetic field, a current-carrying loop experiences a force and rotates. The Fleming left-hand rule specifies which way the loop will rotate.
3. What is the role of the split ring in an electric motor?
Answer: The split ring serves as a commutator in an electric motor. After every half-rotation of the coil, the commutator changes the direction of the current flowing through the coil. The coil keeps spinning in the same direction as a result of this current reversal.
Intext / page 247
1. Explain different ways to induce current in a coil.
Answer: The following list includes various methods for creating current in a coil:
- A coil develops an induced current if the magnetic field around it is altered. A bar magnet can be used to accomplish this by moving it closer or farther from the coil.
- A second induced current is created in a coil if it is moved in a magnetic field.
- A coil rotating in a consistent magnetic field might also induce current inside the coil.
Intext / page 248
1. State the principle of an electric generator.
Answer: The electromagnetic induction theory serves as the foundation for an electric generator. An induced voltage develops between the coil’s ends when a rectangular coil is rotated in a consistent magnetic field.
2. Name some sources of direct current.
Answer: Some sources of direct current are a cell, a battery and a D.C. generator.
3. Which sources produce alternating current?
Answer: A.C. generator and invertors (used in house for emergency power supply) produces alternating current.
4. 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
Answer: (c) half revolution
Intext / page 249
1. Name two safety measures commonly used in electric circuits and appliances.
Answer: Two safety measures are:
- Use of earth wire and proper earthing
- Use of fuse
2. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Answer: Given,
P = 2 kW = 2000 W
V = 220 V
I (current drawn) = P / V
= 2000 W / 220 V
= 9.09 A
Due to the oven’s 9 A current draw, which exceeds the domestic electric circuit’s 5 A current rating, the circuit will be damaged due to overloading and overheating.
3. What precaution should be taken to avoid the overloading of domestic electric circuits?
Answer: The following precautions should be taken to prevent domestic circuits from becoming overloaded:
- Too many appliances shouldn’t be connected to a single outlet.|
- Using too many appliances at once is not recommended.
- Fuse should be connected in the circuit; faulty appliances shouldn’t be connected in the circuit.
Exercise
1. Which of the following correctly describes the magnetic field near a long straight wire?
Answer: (d) The field consists of concentric circles centred on the wire.
2. The phenomenon of electromagnetic induction is (a) the process of charging a body.
Answer: (c) producing induced current in a coil due to relative motion between a magnet and the coil.
3. The device used for producing electric current is called a
Answer: (a) generator
4. The essential difference between an AC generator and a DC generator is
Answer: (d) AC generator has slip rings while the DC generator has a commutator
5. At the time of short circuit, the current in the circuit
Answer: (c) increases heavily
6. State whether the following statements are true or false.
Answer: (a) An electric motor converts mechanical energy into electrical energy. (False)
(b) An electric generator works on the principle of electromagnetic induction. (True)
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines. (True)
(d) A wire with a green insulation is usually the live wire of an electric supply. (False)
7. List three sources of magnetic fields.
Answer: The following are three ways to create a magnetic field:
- A permanent bar magnet or a horse-shoe magnet can be used to create a magnetic field at the desired location.
- A magnetic field is created around a current-carrying circular coil or a straight conductor.
- Current flow in a solenoid is a very effective way to create magnetic fields.
8. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current–carrying solenoid with the help of a bar magnet? Explain
Answer: Each turn of a solenoid coil produces a magnetic field that is uniform in direction when current is passed through it. The resultant magnetic field as a result grew very strong and regular. The field lines inside the solenoid are parallel, straight lines that run along the solenoid’s axis. The solenoid acts like a bar magnet as a result. The solenoid has two ends, one of which acts as the magnetic North Pole and the other as the South Pole. The magnetic poles created in a solenoid can be identified.
The current-carrying solenoid’s terminal, which pulls a bar magnet’s north pole but repels its south pole, is acting like the south magnetic pole. The other end of a bar magnet behaves like the north magnetic pole because it repels the north pole but attracts the south pole. It’s because opposite poles attract one another while like poles repel one another.
9. When is the force experienced by a current–carrying conductor placed in a magnetic field largest?
Answer: When a current-carrying conductor is placed in a magnetic field, the force it experiences is greatest when it is placed perpendicular to the magnetic field.
10. Give the factors on which, magnetic field produced by a current carrying solenoid depends.
Answer: The following variables affect how strong a magnetic field created by a current-carrying solenoid will be:
i. The solenoid’s number of turns determines the strength of the magnetic field that is generated.
ii. The magnetic field produced depends on the amount of current flowing through the solenoid.
iii. The magnetic field can be multiplied thousands of times by winding the coil around a soft iron cylinder, or core.
11. (a) A compass needle gets deflected when brought near a current carrying conductor. Why?
(b) What happens to the deflection of the needle when the current in the conductor is increased?
Answer: (a) A magnetic needle deflects when it is brought into close proximity to a conductor that is carrying current because the magnetic field of the conductor acts as a force on the magnetic needle, causing it to move from one direction to the other.
(b) The needle of the compass will deflect more than it did earlier when the wire’s current is increased.
12. Explain why a fuse should be joined with the live wire and not with the neutral wire to a domestic circuit.
Answer: The power is delivered to the home via a live wire from the supplier and is returned via a neutral wire in a domestic circuit. As a result, the fuse needs to be connected to the live wire in order to prevent damage to the appliance from overloading.
13. Name and state the rule to determine the direction of a force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it. Name a device that uses current carrying conductor and magnetic field.
Answer: The Fleming left-hand rule is the name of it. According to this theory, the thumb represents the direction of force, the forefinger the direction of the magnetic field, and the middle finger the direction of the applied current if our forefinger, middle finger, and thumb are stretched out until they are all perpendicular to one another.
An electric motor is a machine that makes use of a current-carrying conductor and magnetic field.
14. Can a freely suspended current carrying solenoid stay in any direction? What will happen when the direction of current in the solenoid is reversed?
Answer: No, because it behaves like a bar magnet, the current-carrying solenoid falls freely and stays in the North-South direction. A solenoid’s direction of current flow also changes when the current flow is reversed through it.
15. What does the direction of thumb indicate in the right hand thumb rule? In what way this rule is different from Fleming’s left hand rule?
Answer: The thumb in Fleming’s left-hand rule gives the direction of force experienced by a current-carrying conductor placed in an external magnetic field, while the thumb in the right hand rule indicates the direction of current in the straight conductor held by curled fingers.
16. 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: The current will flow in the opposite direction, from the front wall to the back wall or towards us, because the electron beam is moving from our back wall to the front wall in this instance. The force is coming from our right side in the direction of deflection.
We now know two things: The force is directed to our right side, and the direction of the current is from the front towards us.
Let’s now hold our left hand’s forefinger, middle finger, and thumb at a 90-degree angle to one another. Now, we position the hand so that the thumb faces the right side and the middle finger points in the direction of the current (in the direction of force). Our forefinger will now be pointing vertically downward if we look at it. The magnetic field is vertically downward because the direction of the forefinger indicates the direction of the magnetic field.
17. Draw a labelled diagram of an electric motor. Explain its principles and workings. What is the function of a split ring in an electric motor?
Answer: Electric Motor: An electric motor is a device that transforms electrical energy into mechanical energy. It is utilised in machines like fans.
Principles: Electric motors operate under the principle of the force exerted by a conductor carrying current in a magnetic field. The two opposing forces are equal and complementary. They cause rotational motion because they operate along distinct lines.
How an electric motor operates: The coil ABCD is horizontal when current begins to flow. The armature coil’s current flows in two different directions: from A to B in arm AB and from C to D in arm CD. The Fleming left hand law can be used to determine the direction of the force acting on the coil.
This law reveals that the coil is pushed downward by the force applied to part AB. While the part CD is being pushed upward by the force applied to it. In this way, these two forces, which are equal and in opposition to one another, combine to rotate the coil anticlockwise.
The current in the coil is stopped when the coil is vertical because the brushes X and Y would come into contact with the commutator’s centre. Even though the current is cut off, momentum causes the coil to return to its horizontal position. The polarity of the commutator also changes after half rotation because Q now contacts brush X and P contacts brush Y. As a result, the force now acts downwardly on arm AB and upwardly on arm CD, and once more a couple of forces are created that cause the coil to rotate in a clockwise direction. The coil rotates as this procedure is carried out repeatedly until current is flowing through it.
18. Name some devices in which electric motors are used.
Answer: Appliances like electric fans, washing machines, mixers, grinders, blenders, computers, MP3 players, etc. use electric motors..
19. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil (ii) withdrawn from inside the coil (iii) held stationary inside the coil?
Answer: (i) A momentary deflection in the galvanometer is seen as a bar magnet is pushed into the coil, indicating the generation of a momentary current in the coil.
(ii) The galvanometer deflects in the opposite direction when the bar magnet is removed from the coil, indicating the production of an opposing current.
(iii) The galvanometer does not deflect when the bar magnet is kept stationary inside the coil, indicating that no current is generated in the coil.
20. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
Answer: Yes, the coil B will experience some current induction. A small amount of current is induced in coil B when the current in coil A is changed. The magnetic field lines connecting coils A and B change as a result of a change in current in coil A. In coil B, this creates induced current.
21. 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 conductor placed 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 conductor carrying the current is held in the right hand with the thumb pointing in the direction of the current, the magnetic field’s direction will be indicated by the curl of the fingers.
(ii) The Fleming left hand rule: Extend the thumb, middle finger, and forefinger of the left hand so that they are all perpendicular to one another. The thumb will point in the direction of force in the conductor if the forefinger points in the direction of the magnetic field, the middle finger in the direction of current.
(iii) The Fleming right hand rule states that the thumb, forefinger, and middle finger of the right hand should all be stretched out parallel to one another. The middle finger points in the direction of current induced in the conductor if the thumb and forefinger point in the direction of the conductor’s motion and magnetic field, respectively.
22. Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
Answer: Principle: The electromagnetic induction theory serves as the foundation for the electric generator. A coil’s number of magnetic field lines changes when it is rotated in relation to a magnetic field. This causes a current to be induced in the coil, and Fleming’s right hand rule can be used to determine its direction.
Working: The magnetic lines of force are cut through when the armature coil ABCD rotates in a magnetic field created by the permanent magnets.
An induced electromagnetic force is generated in the associated magnetic field as a result of the armature coil’s rotation. With the aid of Fleming’s right hand rule, it is possible to determine the direction of this induced electromotive force or current.
Brush B1 moves the current in one direction during the first half of the cycle, and brush B2 moves it in the opposite direction during the second. This procedure keeps going. As a result, the current generated is alternating.
23. When does an electric short circuit occur?
Answer: When live and neutral wire come into direct contact with one another in a domestic circuit without any resistance, a short circuit results. When the circuit’s resistance drops to zero, an excessive amount of current begins to flow through it.
24. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Answer: A safety measure known as earth wire offers a low resistance conducting path for the current. When the live wire comes into direct contact with an appliance’s metallic cover due to excessive heat or wear and tear, an electric shock may result from touching the metal. The metallic component is connected to the earth through a three-pin plug to prevent shock, causing current to flow to the earth in the event of a short circuit.
Metallic appliances must be earthed in order to ensure that, in the event of a current leak in the metallic cover, the potential of the appliance equals that of the earth. The earth has no potential at all. The person using the appliance won’t receive an electric shock as a result.
Tick (✓) the correct option
1. The strength of the magnetic field of a solenoid does not depend upon:
Answer: (c) core of the coil
2. The magnetic field around a current carrying conductor is:
Answer: (b) Inversely proportional to r
3. Inside a current carrying solenoid the magnetic lines of force are:
Answer: (b) along the axis of the solenoid and parallel to each other
4. A current carrying wire produces:
Answer: (b) a magnetic field
5. The direction of induced potential difference is given by:
Answer: (d) Fleming’s right hand rule
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