Class 10 Science Chapter 12 Question Answers - Magnetic Effects of Electric Current

Ques 1: How will you find out the direction of the magnetic field produced by current-carrying conductor?
Ans: The direction of lines of force of the magnetic field produced by a straight wire carrying current is obtained by Maxwell’s right hand thumb rule. According to Maxwell’s right-hand thumb rule, “Imagine that the current carrying wire is in the right hand so that the thumb points in the direction of current, then the direction in which the fingers encircle the wire gives the direction of magnetic lines of force around the wire.
Imagine a current carrying wire AB in which the current is flows vertically upwards. To find out the direction of magnetic lines of force produced by this current, we imagine the wire AB to be held in the right hand, so that the thumb points in the direction of current towards A. Now, the direction in which the fingers are folded gives the direction of the lines of force. In this case the fingers are folded in the anti-clockwise direction, so the magnetic lines of force are also in the anti-clockwise direction.

Ques 2: What type of core should be put inside a current-carrying solenoid to make an electromagnet?
Ans: A soft iron core is placed inside a solenoid to make an electromagnet. When a soft iron core is placed inside a solenoid, then the strength of the magnetic field becomes very large because the iron core gets magnetized by induction. This combination of a solenoid and a soft iron core is called an electromagnet.

Ques 3: Distinguish between a bar magnet and an electromagnet.
Ans: 


Ques 3: Explain what is short-circuiting and overloading in an electric supply.
Ans: Short-circuiting: If the plastic insulation of the live wire and neutral wire gets torn, then the two wires touch each other. This touching of the live wire and neutral wire directly is known as short-circuiting. The current passing through the circuit formed by these wires is very large and consequently a high heating effect is created which may lead to fire.
Overloading: The current flowing in domestic wiring at a particular time depends on the power ratings of the appliances being used. If too many electrical appliances of high power rating are switched on at the same time, they draw an extremely large current from the circuit. This is known as overloading. Due to this large current flowing through them, the copper wires of household wiring get heated to a very high temperature and may lead to fire.

Ques 4: Give two reasons why different electrical appliances in a domestic circuit are connected in parallel.
Ans: (i) If one of the appliances is switched off or gets fused, there is no effect on the other appliances and they keep on operating.
(ii) The same voltage of the main line is available for all electrical appliances.

Ques 5: Why is a fuse wire made of a tin-lead alloy and not copper?
Ans: A fuse wire is made of tin alloy because it has low melting point, so that it may melt easily, whereas a copper wire cannot be used as a fuse wire because it has a high melting point due to which it will not melt easily when a short circuit takes place.

Ques 6: What is a fuse wire? What is the advantage and disadvantage of using a thick fuse wire?
Ans: A fuse is a very important device used for protecting electric circuits. It is a wire made out of a metal like tin or tin alloy having a very low melting point.
When a high current flows through a circuit, the fuse wire gets heated or melts due to short-circuiting or overloading. Hence the circuit is broken and the current stops flowing. This saves all the appliances of the circuit.

Ques 7: What are magnetic field lines? How is the direction of a magnetic field at a point determined? Mention two important properties of the magnetic field lines.
Ans: The space surrounding a magnet in which magnetic force is exerted, is called a magnetic field. Magnetic field lines are the lines that are drawn at every point indicating the direction in which a north pole would move if placed at that point. They are determined by placing an imaginary hypothetical north pole at that point and finding the direction in which it would move due to the magnetic field at that point. A compass needle gets deflected when placed near a magnet due to the magnetic force exerted by the magnet on it.
Some important properties of magnetic field lines are:
(i) The tangent drawn at any point on the field line indicates the direction in which a north pole would move if placed at that point.
(ii) The relative strength of the field is proportional to the degree of closeness of the lines. The more clustered they are, the stronger the field in that region.
(iii) The magnetic field lines never intersect. This is because a pole can move only in zone direction and if the lines intersect they would have to move in two direction simultaneously which is impossible.

Ques 8: Draw a rough sketch of the pattern of field lines due to a
(i) current flowing into a circular coil and
(ii) solenoid carrying current.
Ans:


Ques 9: 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.
(iv) Current induced in a circuit by the changing magnetic flux due to the motion of a magnet.
Ans: (i) The direction of a magnetic field produced around a current-carrying conductor can be obtained by using Maxwell’s right-hand thumb rule. It states that “if you hold the current carrying wire in your right hand with your thumb pointing in the direction of the magnetic field then the fingers will wrap around the conductor in the direction of the magnetic field lines due to the conductor”.
(ii) The direction of the force experienced by a straight conductor carrying current placed in a magnetic field is determined using Fleming’s left hand rule. It states that “if you stretch the forefinger, the central finger and the thumb of your left hand mutually perpendicular to each other, the forefinger points in the direction of the magnetic field and the central finger points in the direction of current, and the thumb points in the direction of force acting on the conductor”.
(iii) The direction of the current induced in a circuit by changing the magnetic flux due to motion of a conductor is given by Fleming’s right hand rule. It states that “if you hold the forefinger, the central finger and the thumb of your right hand mutually perpendicular to each other, the forefinger indicates the direction of the changing field / flux, the thumb indicates the direction of motion of the conductor and the middle finger gives the direction of the induced current”. This phenomenon is called electromagnetic induction.

Ques 10: What is the function of an earth wire? Why is it necessary to earth the metallic appliances?
Ans: To avoid electric shocks, the metal body of an electrical device is ‘earthed’. A wire called ‘earth wire’ is used to connect the metal body of the electrical device to the earth, which is at zero potential. In household circuits, we have three wires, the live wire, the neutral wire and the earth wire. One end of the earth wire is connected to the device and the other end of the wire is connected to the earth. We now say that the device is “earthed” or “grounded”. Usually the three wires are connected to a three-pin plug. The neutral wire or the earth connection carries the high current to the earth from the device and prevents an electric shock.