Very Short Answer Questions (1 Mark)
1. Magnetic field lines determine
The shape of magnetic field
Only the direction of magnetic field
Only the relative strength of the magnetic field
Both the direction and the relative strength of magnetic field
Ans: (d) Both the direction and the relative strength of magnetic field
2. A device for producing electric current is called a
Galvanometer
Motor
Generator
Ammeter
Ans: (c) Generator
3. At the time of short circuit, the current in the circuit
vary continuously
reduced considerably
increases heavily
does not change
Ans: (c) increases heavily
4. The magnetic field near a long straight wire is described by
Straight field lines parallel to the wire.
Straight field lines perpendicular to the wire.
Connective circle centred on the wire.
Radial field lines starting from the wire.
Ans: (c) Connective circle centred on the wire.
5. A current carrying conductor placed in magnetic field experiences a force. The displacement of the conductor in magnetic field can be increased by
Decreasing the magnetic field.
Decreasing the current in the conductor.
Increasing the magnetic field.
None of the above.
Ans: (c) Increasing the magnetic field.
6. A positively charged particle say an alpha particle projected towards west is deflected toward north by a magnetic field. The direction of the magnetic field is
upward
downward
towards south
towards east
Ans: (a) upward
7. In which position the force on conductor is maximum when it uniform magnetic field? is placed in
Ans: When the conductor is parallel to the field
8. How can it be shown that magnetic field exist around a wire carrying current?
Ans: By using a magnetic compass that displays deflection.
9. How can a solenoid be used to magnet a steel bar?
Ans: By placing a steel bar into the solenoid and turning on the electricity.
10. Why can’t two magnetic field lines ever intersect?
Ans: If this is the case, there will be two separate magnetic field directions at the site of intersection, which is not feasible.
11. Can 5A fuse be used in wire carrying 15 A current? Why?
Ans: Because they'd both be useless at managing the quantity of current flowing if that happened.
12. Give the factors that affect strength of magnetic field at a point due to a straight conductor carrying current.
Ans: Perpendicular distance between that point and the conductor, magnitude of electric content.
13. Where do we connect a fuse: with live wire or with neutral wire?
Ans: It is always wired with live electricity.
14. Name any two devices which use permanent magnets.
Ans: Loudspeaker, Motor, Galvanometer, voltmeter.
15. What is the pattern of the magnetic field lines around a straight conductor carrying current?
Ans: Concentric circles
16. If the current is flowing in the direction of advancement of screw, then what is the direction of magnetic field lines?
Ans: Magnetic field will be directed inwards.
17. How can you say that the magnetic field is uniform inside the solenoid?
Ans: Because the field lines inside the solenoid are parallel.
18. Which property of a proton will change while it moves freely in a magnetic field?
Ans: Momentum or Velocity.
19. According to Flemings right hand rule, which part of right hand indicate the movement of conductor?
Ans: Thumb
20. If the no. of turns of a circular current carrying coil are doubled, then how will the magnetic field produced by it changes?
Ans: Doubled
Short Answer Questions (2 Marks)
1. State two properties of magnetic lines of force?
Ans: The two properties of magnetic lines of force are-
i. The strength of the magnetic field is proportional to the closeness of the lines.
ii. They can never cross i.e. the field is unique at any point in space.
2. Why does a compass needle deflect when brought near a bar magnet?
Ans: A compass needle deflected when brought near a bar magnet due to the magnetic field of the bar magnet.
3. The magnetic field lines in a given region are uniform. Draw a diagram to represent.
Ans: The magnetic field lines in a given region are uniform when they are represented in the same direction.
4. Write two ways to induce current in a coil?
Ans: The two ways to induce current in a coil are-
i. By moving a bar magnet toward or away from the coil current is induced.
ii. By moving a coil rapidly between the two poles of a horseshoe magnet.
5. Why do not two magnetic field lines intersect each other?
Ans: If two magnetic field lines intersect each other then there will be two directions of magnetic field, which is not possible. Thus, they do not intersect each other.
6. Name and state rule used to determine the direction of magnetic field produced around a straight conductor carrying current?
Ans: Right hand thumb rule is used to determine the direction of magnetic field produced around a straight conductor carrying current. It states that if we hold the current-carrying conductor in our right hand such that the thumb points the direction of the current, then the direction in which the fingers encircle, gives the direction of magnetic lines.
7 What is electric fuse? Where is it connected in a circuit?
Ans: Electric fuse is a safety device which is used to limit the current in an electric circuit which is made up of a wire made of copper or aluminium or a tin lead alloy. It is always connected in series at the beginning of the circuit.
8. State the factors on which strength of magnetic field at a point due to a current carrying conductor depends?
Ans: The factors on which strength of magnetic field at a point due to a current carrying conductor depends are-
i. It is directly proportional to the amount of current (I) flowing through the conductor.
ii. It is inversely proportional to the distance (r) from the current carrying conductor.
9. What is an electromagnet? Write two uses of an electromagnet?
Ans: They are the type of magnet in which the magnetic field is produced by an electric current i.e. when current is passed through a solenoid it behaves as a magnet and is called an electromagnet.
The two uses of an electromagnet are-
i. Used in electrical devices like motors, generators etc.
ii. Used to lift heavy iron pieces.
10. State and define S.I unit of magnetic field?
Ans: The S.I unit of magnetic field is Tesla (T). It states that 1meter long conductor carrying 1 ampere current experiences 1 Newton force, when placed perpendicular to the direction of magnetic field then the magnetic field strength is 1 Tesla.
Short Answer Questions (3 Marks)
1. What is the function of an earth wire? Why is it necessary to earth metallic casing of electric appliances?
Ans: The earth wire is used for the safety measures that have green insulation and is connected to a metal plate deep in the earth near our houses. Appliances like the electric press, toaster, table fan, refrigerator, etc have the metallic body that needs to connect to the earth wire this will provide a low resistance path for the. Thus, if any leakage of current occurs to the metallic body of the appliance it keeps potential to that of the earth, and this may prevent the severe electric shock.
2. We know a current-carrying conductor placed in a magnetic field experience a force due to which the conductor moves. How do we think the rod displaces if
(a) current in the rod is increased
Ans: Force acting on the current-carrying conductor depends on the strength of the magnetic field, amount of current flowing in the conductor, and length of the conductor. Therefore, when the current in the rod increase then the force also increases hence displacement of the rod increases.
(b) a stronger horseshoe is inserted
Ans: Force acting on the current-carrying conductor depends on the strength of the magnetic field, amount of current flowing in the conductor, and length of the conductor. Therefore, when a stronger horseshoe magnet is inserted, the magnetic field increases. So, force increase. Hence displacement increases.
(c) length of the rod is increased
Ans: Force acting on the current-carrying conductor depends on the strength of the magnetic field, amount of current flowing in the conductor, and length of the conductor. Therefore, when the length of the rod increase, force increases, and hence displacement increases.
3. What is the principle of electric motor?
Ans: Electric motor is a rotating device that can convert electrical energy into mechanical energy. Which works on the principle that a current-carrying conductor placed perpendicular to a magnetic field experience a force.
State the function of,
(i) split ring
Ans: It acts as a commutator. The split ring reverses the direction of current through the coil after every half rotation and thus the direction of force is also reserved. As a result, the dc motor continues to rotate in the same direction.
(ii) field magnet used in the electric motor.
Ans: Field magnet used in the electric motor provided a strong magnetic field.
4. State three factors on which magnetic field produced by a current-carrying solenoid depends.
Ans: The three factors on which the magnetic field produced by a current-carrying solenoid depends are the strength of the current flowing through the solenoid, the number of turns of the wire of the solenoid, and the nature of the material inside the solenoid.
5. What is a solenoid? Draw magnetic field lines showing the magnetic field inside and outside the current-carrying solenoid?
Ans: A solenoid is a coil that has many circular turns of insulated copper wire, which are arranged closely in the shape of a cylinder.
6. (a) Name four appliances wherein an electric motor is used as an important component. In what respect is it different from a generator?
Ans: The four appliances which have electric motor inside them are Mixers, washing machines, refrigerators, and blenders. In electric motor electrical energy is converted into mechanical energy whereas, in an electric generator mechanical energy is used to produce electricity.
(b) Define the terms used in the generator
(i) armature
Ans: Armature is a coil of a large number of turns of insulated copper wire wound over a soft iron core.
(ii) slip rings
Ans: Rings made up of brass that rotates along with the coil and helps in reversal of the direction of the current.
(iii) brushes
Ans: Brushes are made up of carbon which is pressed against the slip rings and are connected to an external circuit where output is obtained.
7.(a) What is the standard colour code followed for
(i) live
Ans: red
(ii) neutral and
Ans: black
(iii) earth wires used in electric circuits?
Ans: green
(b) Which part of an electric appliance is earthed and why?
Ans: The metallic case of an electrical appliance is earthed because metals are good conductors of electricity and in case of current leakage i.e. live wire touches the metallic case of an appliance and then due to proper earthing all the excess amount of current flows down to the earth and thus, we can prevent ourselves from an electric shock.
8.(a) What is short-circuiting?
Ans: Overloading occurs when live and neutral wires come into direct contact, in that case, the current in the circuit increases abruptly. This is called short-circuiting.
(b) What is overloading? How can you avoid overloading?
Ans: Overloading means a huge amount of current flows in the circuit. It can occur when live and neutral wires come into direct contact. It can be avoided by not using too many appliances in a single socket and by using a fuse in the circuit which can prevent damage to the appliances and the circuit.
9. Define electromagnetic induction? Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in the coil B? Explain.
Ans: Electromagnetic induction is a process by which the production of induced current in a conductor due to the change in the magnetic field in another conductor. When the current in first coil A is changed, the magnetic field associated with coil A also changes. Thus, the magnetic field lines around the secondary coil B will also change. Hence the change in magnetic field lines associated with the secondary coil B will induce electric current in it.
10. List the properties of magnetic lines of force.
Ans: Properties of magnetic field lines of force are as follows:
i. Outside a magnet, the field lines are directed from the N-pole of the magnet towards the S-pole, and inside the magnet, lines are directed from S-pole to N-pole.
ii. Magnetic field lines are closed curves.
iii. No two magnetic field lines intersect each other.
iv. The density of magnetic lines decreases, when the distance between the poles increases.
11. In activity 13.7, how do we think the displacement of rod AB will be affected if
(i) current is rod AB is increased,
Ans: If the current in rod AB is increased then its displacement will also increase.
(ii) a stronger horseshoe magnet is used, and
Ans: If a stronger horseshoe magnet is used then the displacement of rod AB will also increase.
(iii) length of the rod AB is increased?
Ans: If the length of the rod AB is increased, the force acting on it will increase hence, displacement of the rod also increases.
12. State Fleming’s left-hand rule.
Ans: Fleming’s left-hand rule states that stretch the forefinger, the central finger, and the thumb of your left hand in a way they mutually perpendicular to each other. If the forefinger shows the direction of the magnetic field and the central finger that of the current, then the thumb will point towards the direction of motion of the conductor or the force acting.
Long Answer Questions (5 Marks)
1. Current- time graph from two different sources are shown in the figure
(i) Name the type of current shown by graph (A) and (B)?
Ans: Graph A represents direct current and graph B represents alternating current.
(ii) Name any one source of shown by (A) and (B)?
Ans: Source of (A) can be dry cell and Source of (B) can be AC generator.
(iii) What is frequency of current in case (B)?
Ans: As graph B represents the alternating current the frequency is given by, 50hz
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