Electric Fuse - Advantage and Disadvantage

Fuses

A Fuse is a small piece of metal inserted in a fuse circuit, which melts on excessive flow through this and thus breaks the circuit.

Fuse element is usally made of low melting point,high conductive material and least fall due to oxidation e.g.,sliiver,copper etc.  

Advantages
(i)It is the cheapest from of protection available.
(ii)It requires no maintenance.
(iii)Its operation is inherently completely automatic unlike a circuit breaker which requires an elaborate equipment for automatic action.
(iv)It can break heavy short-circuit current without noise or smoke.
(v)The smaller size of fuse element impose a current limiting effect under short-circuit conditions.
(iv)The inverse time-current characteristic of a fuse makes its suitable for overcurrent protection.
(vii)The minimum time of operation can be made much shorter than with the circuit breakers.
 
Disadvantages
(i)Considerable time is lost in rewiring or replacing a fuse after operation.
(ii)On heavy short-circuit,discrimination between fuses in series cannot be obtainted unless there is sufficient difference in the sizes of the fuses concerned.
(iii)The current-time characteristic of a fuse cannot always be co-related with that of the protected apparatus.   

DC Circuit-short Question and Answer

 TOPIC- DC Circuit -Short Question and Answer

Q.1.Why are domestic appliances connected in parallel?

Ans.The domestic appliances are connected in parallel due to the following reasons:

(i)The domestic appliance are rated for the same voltage (i.e.,230V) but different power. When

connected in parallel,the performance of each appliance become independent of the other.Thus a 230V, 250W TV receiver can be operated independently in parallel with a 230V,100W lamp.

(ii)If a break occurs in any one of the branch circuits,it will have no effect on the other branch circuit.

Q.2.Why does a cell posses internal resistance?

Ans.When current flows through a cell, it meets opposition from the electrodes and the electrolyte.

This opposition to current offered by the cell is called its internal resistance.

Basic Electrical - Short Question and Answer

TOPIC : Basic Electrical Short Question and Answer 

Q.1.Why does a positive charge attract a negative charge ?

Ans. It is the tendency of every body to have minimum electric potential i.e., to obtain zero potential. A positive charge means deficit of electrons while the negative charge indicates excess of electrons. Consequently, positive and negative charges attract each other to have minimum electric potential.  

Q.2. A wire is carrying current. Is it charged?

Ans. No. The current in a wire is due to the drifting of free electrons in a definite direction. But the number of electrons in the wire at any instant is equal to the number of protons. Hence, the net charge on the wire is zero.

Electrical Illumination Fill In The Blanks

 FILL IN THE BLANKS

1. Visible light has wavelength between 4000 A and 7500 A.

2. Human eye is most sensitive for a wave length of 5500.

3. The color corresponding to wavelength 5500 A is Yellow, Green. 

4. Lamp efficiency is expressed in Lumens per watt.

Electric Illumination are true (T) or false (F)

TRUE AND FALSE

1. Carbon arc lamps needs frequent adjustment and replacement of carbon rod.--T

2. Lumen method takes into account the inter-reflections of light inside a room.--T

3. Luminairs are generally categorized as industrial, commercial or residential.--T

4. Lenses with prismatic patterns refract light sources to disperse the rays or to direct them most effectively.--T

Multiple Choice Questions of Electric Illumination

MCQ of Illumination

1. Radiant efficiency of the luminous source depends on
(A) shape of the source
(B) temperature of the source
(C) wavelength of light rays
(D) all of the above.

2. Light waves travel with a velocity of
(A) 3 x 10¹⁰cm/s
(B) 3 x 10¹²cm/s
(C) 3 x 10¹⁵ cm/s
(D) 3 x 10¹⁸ cm/s

Illumination Engineering

Electrical Illumination Definitions

Light

it is defined as the radiant energy from a hot body which produce the visual sensation upon human eye. It is usually denoted by Q, expressed in lumen-hours and is analogous to watt-hours.

Luminous Flux(F or Ф)

It is defined as the total quantity of light energy per second from a luminous body.It is represented by symbol F or Ф and unit is lumen.

Approximate relation between lumen and electric unit of power i.e. watt is given as

 1lumen=0.0016 watt(approx).