Electrical Engineering mcq-Basic Concept MCQ questions answers-1

Electrical Engineering-Basic Concept MCQ questions answers

1.       The mass of a proton is about 1837 times the mass of electron.

2.       The electrons in the last orbit of an atom are called valance electrons.

3.       In the number of valance electrons of an atom is less than 4, the substance is usually conductor.

4.       In the number of valance electrons of an atom is more than 4, the substance is usually

              An insulator.

5.      In the number of valance electrons of an atom is less than 4, the substance is usually a  
       semi-  conductor.

6.       The electric current is due to the flow of both positive and negative charges.

7.       E.M.F in a circuit maintains potentials difference.

8.       The electric current in a metallic conductor is due to the flow of electrons only.

9.        Potentials difference has the unit of energy.

10.    The electric current in a liquid is due to the flow of negative and positive ions both.

          

Why Insulator have negative temperature co-efficient of resistance

Why Insulator have negative temperature co-efficient of resistance

If insulators temperature rises it creates more free electrons than existed cooler state. These often increase the number of free electrons than offsetting the drift movement disorder caused by the increased molecular activity. So insulators resistance decreases with increasing temperature. For example, insulators have a negative temperature coefficient of resistance.

Why conductors have positive temperature co-efficient of resistance

Why conductors have positive temperature co-efficient of resistance?


Increase in temperature of a substance to cause two effects: 

a. This causes the molecules to vibrate faster, thus preventing the movement of free electrons in the material. 

b. It can break some bonds, releasing free electrons. With the rise in temperature of wins, no increase in the number of free electrons and the sole effect of temperature rise is to increase the resistance due to the increased molecular vibration. Winners then have a positive temperature co-efficient of resistance. Example resistance increases with temperature.

Is ohm’s law true for all conductors

Is ohm’s law true for all conductors?

No, it is true only for metallic conductors provided physical conditions do not change.

Unit of Energy

Unit of Energy

Volt is the unit of energy. Volt is also unit of electric potentials.

Electric Potentials:  V= work done/Q

                                      =W/Q

So, the unit of electric potentials is Joules/C. Now Joules/C is called as volt