Answer The Following Question.
1. Draw magnetic field around a bar magnet.
Ans : Magnetic field lines are as follows:
2. List the properties of magnetic lines of force.
Ans: Properties of Magnetic Lines of Force:
Outside a magnet, magnetic lines of force travel from the North (N) pole to the South (S) pole, and inside the magnet, they travel from the South (S) pole to the North (N) pole.
Magnetic field lines form closed loops.
Magnetic field lines never intersect each other.
The strength of the magnetic field is indicated by the closeness of the magnetic lines of force — the closer the lines, the stronger the field.
3. Why don’t two magnetic lines of force intersect each other?
Ans: Two magnetic lines of force do not intersect because, at the point of intersection, there would be two different directions of the magnetic field, which is not possible. The magnetic field has only one direction at any given point.
4. 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.
Ans : As per right-hand rule, we find that inside the loop, the magnetic field lines are directed perpendicular to the plane of paper in the inward direction. Outside the loop magnetic field lines are directed out of the plane paper.
5. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Ans: The uniform magnetic field is represented by parallel equispaced lines of equal length as follows:
6. Choose the correct option:
The magnetic field inside a long straight solenoid-carrying current
(a) Is zero.
(b) Decrease as we move towards its end.
(c) Increase as we move towards it end.
(d) Is the same all points.
Ans : (d) is the same at all points.
7. Which of the following property of a proton can change while it moves freely in a magnetic field?
(a) mass
(b) speed
(c) velocity
(d) momentum
Ans : (c), (d) Velocity as well as momentum will change.
8. In activity 12.7, how do we think the displacement of rod AB will be affected if (i) current is rod AB is increased, (ii) a stronger horse shoe magnet is used, and (iii) length of the rod AB is increased?
Ans: The displacement of rod AB in activity 12.7 will be affected as follows:
(i) If the current in rod AB is increased, the magnetic force acting on the rod will increase, leading to a greater displacement.
(ii) If a stronger horseshoe magnet is used, the magnetic field strength increases, which will also increase the force on the rod, causing a larger displacement.
(iii) If the length of rod AB is increased, the force exerted on the rod will increase, since the force depends on the length of the conductor in the magnetic field, leading to a greater displacement.
9. 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
Ans : (d) the direction of magnetic field is vertically upward.
10. Name two safety measures commonly used in electric circuits and appliances.
Ans: Two Safety Measures in Electric Circuits and Appliances:
Electric Fuse:
– Prevents excessive current flow.
– When current exceeds the limit, the fuse melts, breaking the circuit and protecting the appliances.
Earthing:
– Transfers leakage current to the ground.
– Prevents electric shocks and ensures user safety.
11. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220V) that has a current rating of 5.A. What result do you expect? Explain.
Ans : Power rating of electric oven (P) = 2 kW = 2000 W
Current drawn (I) = P/V = 2000/220 = 9.09 A.
As the current rating of domestic electric circuit is only 5A the oven draws a current of 9.09 A. Which is more than the current rating; hence the circuit will be damaged due to overheating / overloading.
12. What precaution should be taken to avoid the overloading of domestic electric circuit?
Ans: Precautions to Avoid Overloading of Domestic Electric Circuit:
Use two separate circuits:
– 5A circuit for low-power appliances like bulbs, fans, and tube lights.
– 15A circuit for high-power appliances like geysers, air coolers, electric irons, and stoves.
Avoid connecting too many appliances to a single socket.
3. Use a fuse of appropriate current rating to prevent overloading and short circuits.
13. At the time of short circuit, the current in the circuit:
(a) reduce substantially
(b) does not change
(c) increase heavily
(d) vary continuously
Ans : (c) increase heavily
14. 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 line
(b) A wire with green insulation is usually the live wire of an electric supply.
Ans :
(a) True
(b) False
15. List three methods of producing magnetic field.
Ans: Three methods to produce a magnetic field are:
Using Permanent Magnets: A magnetic field can be produced by placing a permanent magnet (such as a bar magnet or a horseshoe magnet) at the location where a magnetic field is required.
Current-Carrying Conductors: A magnetic field is produced around a straight conductor or a coil when an electric current flows through it.
Solenoid Method: A very effective way to generate a magnetic field is by passing current through a solenoid, which produces a strong and uniform magnetic field inside the coil.
16. When is the force experienced by a current-carrying conductor placed in magnetic field largest?
Ans: The force experienced by a current-carrying conductor placed in a magnetic field is largest when the conductor is positioned such that its length is perpendicular to the direction of the magnetic field.
Imagine that you are sitting in 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?
An electron beam moving horizontally from the back wall towards the front wall is equivalent to a current flowing in the opposite direction (from front to back). The deflection of the electron beam towards the right side, as observed by the person, indicates the force acting on the moving charges.
Using Fleming’s Left-Hand Rule, where:
The thumb represents the direction of the motion of the electron (current),
The index finger represents the direction of the magnetic field,
The middle finger represents the direction of the force (deflection).
Since the force is towards the right, the magnetic field must be directed vertically downward to satisfy the conditions for the deflection of the electron beam.
17. State the rule to determine the direction of a (i) magnetic field produced around a straight current carrying conductor (ii) force experienced by a current carrying straight conductor (iii) current induced in a coil due to its rotation in a magnetic field.
(i) Magnetic field produced around a straight current-carrying conductor
Ans:
To determine the direction of the magnetic field produced around a straight conductor, we use the Right Hand Thumb Rule. According to this rule, when the right hand is held such that the thumb points in the direction of the current, the curled fingers will show the direction of the magnetic field around the conductor.
(ii) Force experienced by a current-carrying straight conductor
Ans:
To determine the direction of the force experienced by a current-carrying conductor placed in a magnetic field, we use Fleming’s Left-Hand Rule. According to this rule, when the left hand is held with the thumb, index, and middle fingers mutually perpendicular, with the index finger pointing in the direction of the magnetic field and the middle finger in the direction of the current, the thumb will point in the direction of the force.
(iii) Current induced in a coil due to its rotation in a magnetic field
Ans:
To determine the direction of the current induced in a coil rotating in a magnetic field, we use Fleming’s Right-Hand Rule. According to this rule, when the right hand is held with the thumb, index, and middle fingers mutually perpendicular, with the index finger pointing in the direction of the magnetic field and the thumb in the direction of motion of the conductor, the middle finger will point in the direction of the induced current.
18. When does an electric short circuit occurs?
Ans: An electric short circuit occurs when the resistance in an electrical circuit becomes very low, leading to a sudden increase in current flow. This can happen in the following situations:
Overloading the Circuit: Connecting too many appliances to a single socket or connecting high-power-rated appliances to light circuits can cause the circuit’s resistance to decrease, allowing too much current to flow.
Worn Insulation: When the insulation of live and neutral wires undergoes wear and tear, they may touch each other, creating a path with low resistance. This causes an abrupt increase in current, resulting in a short circuit.
In both cases, the increased current can potentially cause damage to appliances, wires, or the circuit, and pose a safety hazard.
19. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Ans: The earth wire serves as a safety measure to prevent electric shocks from metallic appliances. The function of the earth wire is to provide a low-resistance conducting path for any leakage current that may flow to the metallic body of an appliance. Here’s why it is necessary:
Leakage Current Protection: If there is a fault in the appliance and leakage of current occurs, the earth wire provides a safe path for the current to flow to the ground, preventing the appliance body from becoming live.
Safety for Users: By connecting the metallic body of an appliance (such as a heater, electric press, or room cooler) to the earth wire, the potential of the appliance body is made the same as the earth’s potential. This ensures that, even if a person touches the appliance, they will not receive a severe electric shock.
In summary, earthing metallic appliances is necessary to protect users from electric shock and to ensure the safe operation of electrical devices.