NCERT Solution Class 1O Science Chapter 12 Magnetic Effects of Electric Current - Param Himalaya
Page number 196
1. Why does a compass needle get deflected when brought near a bar magnet?
Solution : A compass needle is a small bar magnet when it is brought near a bar magnet its magnetic field lines interact with that of the bar magnet. Hence , a compass needle shows a deflection when brought near the bar magnet
Example 12.1 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?
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.
Page number 200
1. Draw magnetic field lines around a bar magnet.
Solution : Magnetic field lines of a bar magnet emerge from the north pole and terminate at the South pole. Inside the magnet , the magnetic field lines emerge from the South pole and terminate at the north pole.
2. List the properties of magnetic field lines.
Solution :
1. Magnetic field lines events from the north pole and merge at South pole.
2. The direction of field lines inside the magnet is from the South pole to North pole.
3. Magnetic field line do not intersect with each other.
3. Why don’t two magnetic field lines intersect each other?
Solution: if two field lines of a magnet intersect than at the point of intersection the compass needles points in two different direction this is not possible has two field lines do not intersect each other.
Page number 202
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.
Solution :
2. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Solution :
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.
Solution :
Example 12.2 An electron enters a magnetic field at right angles to it, as shown in Fig. 12.14. 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.
Solution :
Answer is option (d). 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.
Page number 203
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.)
(a) mass (b) speed (c) velocity (d) momentum
Solution :
2. 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; and
(iii) length of the rod AB is increased?
Solution :
3. 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
Solution :
Page number 205
1. Name two safety measures commonly used in electric circuits and appliances.
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.
3. What precaution should be taken to avoid the overloading of domestic electric circuits?
Exercise
1. Which one 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 centered on the wire
Solution : (d) The field consists of concentric circles centred on the wire.
2. At the time of short circuit, the current in the circuit:
(a) reduce substantially
(b) does not change
(c) increase heavily
(d) vary continuously
Solution : (c) increase heavily
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 line
(b) A wire with green insulation is usually the live wire of an electric supply.
Solution :
(a) True
(b) False
4. List three methods of producing magnetic field.
Solution : Three methods of producing magnetic fields are as follows:
(a) Magnetic field can be produced by placing a permanent magnet or a horse-shoe magnet at the place, where magnetic field is required.
(b) Magnetic field is produced around a current carrying straight conductor or a current carrying coil.
(c) A very good method to produce magnetic field is due to flow of current in a solenoid.
5. When is the force experienced by a current-carrying conductor placed in magnetic field largest?
Solution : The force experienced by a current carrying conductor placed in a magnetic field is largest when the conductor is placed with its length in a direction perpendicular to that of magnetic field.
6. 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?
Solution : An electron beam moving horizontally from back wall towards the front wall is equivalent to a current flowing in the opposite direction. The deflection of electron beam as seen by the observer is to his right side. On applying Fleming’s left-hand rule we find that the magnetic field is acting in vertically downward direction.
7. 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.
Solution :
(i) To know the direction of magnetic field produced around a straight conductor we make use “Maxwell's Right hand thumb Rule”.
(ii) To find the direction of force experienced by a current carrying straight conductor placed in a magnetic field we make use “Fleming’s left hand rule”.
(iii) For finding the direction of current induced in a coil we use “Fleming’s right hand rule”.
8. When does an electric short circuit occurs?
Solution : If the resistance of an electric circuit becomes very low, then the current flowing through the circuit becomes very high. This is caused by connecting too many appliances to a single socket or connecting high power rating appliances to the light circuits. This results in a short circuit. When the insulation of live and neutral wires undergoes wear and tear and then touches each other, the current flowing in the circuit increases abruptly. Hence, a short circuit occurs.
9. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Solution : The earth wires functions as a safety measure, especially for those appliances that have a metallic body, like heater, electric, press, room cooler etc.
The metallic body of the appliance is connected to the earth wire, which provides a low resistance conducting path for electric current. It ensures that any leakage of current to the metallic body of an appliance keeps it potential same as of earth. As a result, the user would not get severe electric shock, even if he touches the body of appliance.