Magnetic effect of current Worksheet-8

Magnetic effect of current Worksheet-8

 

  1. Why does a current-carrying solenoid when suspended freely rests along a particular direction ?

 

  1. State two ways by which the strength of an electromagnet can be increased.

 

  1. State three factors on which the magnitude of the force on a current-carrying conductor placed in a magnetic field depends. Can this force be zero for some position of the conductor ?

 

  1. A DC motor is rotating in clockwise direction. How can the direction of rotation be reversed ?

 

  1. State two ways by which the speed of rotation of an electric motor can be increased.

 

  1. What are the two main systems of wiring commonly used in household circuits ? Which of the two is better and why?

 

  1. Explain the significance of the following in a house circuiting, (i) kWh Meter (ii) Main Switch.

 

  1. State the principle of an AC generator. What determines the frequency of AC produced in a generator ?

 

  1. What is a switch and how is it connected ?

 

  1. What is the role of each of the three pins in a power plug ?

 

Answer:

  1. A current-carrying solenoid has a magnetic field exactly similar to that of a bar magnet. It behaves like a bar magnet and acquires the directive property, i.e., the property of pointing N-S when it is freely suspended.

 

  1. (i) By increasing the number of turns in the winding on the soft iron core.

(ii) By increasing the strength of the current through the winding.

 

  1. The magnitude of force (F) acting on a conductor of length (L) and carrying a current (I) when placed in a magnetic field of magnitude (B) depends upon I, Land B as follows :

(i) F ∞ I (ii) F ∞ L (iii) F ∞ B          

No force acts on such a conductor when it is placed parallel to the direction of magnetic field.

 

  1. By reversing the direction of current through the coil. This can be achieved by interchanging the terminals of the battery connected to the brushes of the motor.

 

  1. The speed of rotation of an electric motor can be increased by :

(i) Increasing the strength of the current, (ii) increasing the number of turns in the coil.

 

  1. 1. Tree system 2. Ring system.

Ring system of wiring is better than the tree system due to the following reasons :

(a) Every appliance has its own fuse and in case of short-circuiting, only that particular appliance is disconnected from the circuit without affecting the others.

(b) Since the length of wire is considerably small as a single ring feeds the entire house, the cost of wire is reduced.

(c) It is easier to install and maintain.

 

  1. (i) The kWh Meter records the electric energy consumed in kWh.

(ii) The Main Switch is used to cut the connections of the live as well as natural wires simultaneously, thereby cutting electric supply to the whole house.

 

  1. An AC generator is based on the principle of electromagnetic induction. The frequency of AC is determined by the rotation of the coil and is equal to the frequency of rotation of the coil.

 

  1. A switch is a device which can connect or disconnect an electrical appliance in an electric circuit when desired. A switch is always connected to the live wire.

 

  1. The thick pin at the top of a power plug is for earthing. The live pin is on the left and the neutral pin is on the right of the power plug.