Magnetic effect of current Worksheet-9

Magnetic effect of current Worksheet-9

 

  1. State two serious hazards of electricity.

 

  1. What are the two main precautions to be taken while using an electric supply ?

 

  1. Why do iron filings arrange themselves in a definite pattern when sprinkled around a magnet ?

 

  1. What type of magnetic fields do the following magnetic field lines represent ?

 

  1. What types of magnetic fields do the following magnetic field lines represent ?

 

  1. A current through a horizontal power line flows in east to west direction. What is the direction of magnetic field at a point I directly below it and at a point directly above it ? 

 

  1. A current-carrying straight conductor is placed in the east-west direction. What will be the direction of the force experienced by this conductor due to the Earth's magnetic field ? How will this force get affected on :

(a) reversing the direction of flow of current,

(b) Doubling the magnitude of current ?

 

  1. What is the direction of magnetic field at the centre of a circular coil carrying current in

(i) anticlockwise direction (ii) clockwise direction ?

 

  1. What kind of energy transformation takes place in an electric motor ? Name any two devices which use an electric motor as an essential component.

 

  1. How can the magnitude of an induced emf be increased in a generator ?

 

Answer:

  1. 1. If a person accidentally touches the live wire, he may get a severe shock which may prove fatal sometimes. 

2. Short-circuiting or overloading can cause a spark which may lead to fire in a building.

 

  1. Electric supply should be immediately switched off from the main switch in case a person touches a live electric wire or if there is a fire in the house. Electric supply should also be switched off during natural calamities like earthquakes, floods, etc.

 

  1. This is due to the reason that each piece of iron filing becomes a small magnet and experiences a force in a certain direction in the magnetic field due to the magnet.

 

  1. (i) Represents a non-uniform magnetic field which in stronger at point B than at point A.

(ii) Represents a uniform magnetic field as the magnetic field lines are parallel and equidistant from each other.

(iii) Does not represent any type of magnetic field as magnetic field lines do not cross each other.

 

  1. Represents the magnetic field due to a straight current-carrying conductor.

Represents the magnetic field inside a circular conductor carrying current

 

  1. Applying Right-hand Thumb Rule as shown in the figure, we find that the direction of magnetic field (B) at a point P directly above the power line is from south to north whereas  for a point P' below it, magnetic field (B) is ,from north to south.

 

  1. The direction of the Earth's magnetic field is from geographic south to north. Let the direction of current in the conductor be. from west to east. Applying Fleming's left-hand rule, we find, that the direction of the force acting on the conductor will be vertically upwards. (See figure)

(a) By reversing the direction of current (i.e., making it flow from east to west, me direction of force experienced by the conductor will be reversed, i.e., it will now act vertically downwards.

(b) The magnitude of the force is doubled (as F ∞ I)

 

  1. Another Right Hand Thumb Rule, stated differently, can be used to find the direction of magnetic field at the centre of a circular coil carrying current.

It is as follows :

When the current (I) is flowing through a circular coil and if we imagine the fingers of the right hand Curling in the direction of the current, the thumb will point in the direction of the magnetic field (S) at its centre. Applying this rule, we find that for-a circular current-carrying coil with its plane perpendicular to the plane of the paper :

(i) B is along the axis of the coil and is acting upward, (See figure),

(ii) B is along the axis of the coil and is acting downward, (See figure)

 

  1. In an electric motor, electrical energy is converted into mechanical energy. Electric fan, washing machine, refrigerator, mixer and blender use an electric motor as an essential component.

 

  1. (i) By increasing the number of turns in the winding of the armature.

(ii) By increasing the area of the armature.

(iii) By increasing the strength of the magnetic field in which the coil rotates.

(iv) By increasing the speed of rotation of the coil.