Basic Electrical Engineering objectives questions and detail explanation.
1. The flow of current in solids is due to:
(a) electrons (b) atoms
(c) electrons and ions (d) all of these
Solution:- (a)
We know that, an electron is a negatively charge particle having negligible mass revolves in an orbit. Because of very small mass, these are comparatively much lighter than protons therefore, they are greatly influenced by electric or magnetic field. An electron passes following important properties:
1.Charge on an electron,e = 1.602 × 10⁻¹⁹ C.
2. Mass of an electron, m = 9.0 × 10⁻³¹ kg.
3. Radius of an electron, r = 1.9 × 10⁻¹⁵ m.
2. An atom is composed of:
(a) electrons and protons
(b) electrons and neutrons
(c) electrons, protons and neutrons.
(d) none of the
Solution:- (c)
An atom is the smallest particle of the element that cannot usually exist independently and retains all its chemical properties. All matter is made of atoms which are infinitesimally small and each atom constitutes electrons, protons, and neutrons. An atom is said to be electrically neutral when the number of electrons and protons are the same, as they cancel equal and opposite each other electrical force
3. The proton is a ........ particle.
(a) very small and heavy
(b) very very large and light
(c) very large and heavy
(d) any of the above
Solution:- (c)
The proton is a very large and heavy particle as compared to the electron. One or more proton constitutes nucleus of the atom. The proton has positive electrical charge and mass greater than the electron.
4. An electron has a ....... charge.
(a) negative (b) positive
(c) neutral (d) either +ve or -ve
Solution:- (a)
We know that, an electron is a negatively charge particle having negligible mass revolves in an orbit. Because of very small mass, these are comparatively much lighter than protons therefore, they are greatly influenced by electric or magnetic field. An electron passes following important properties:
1.Charge on an electron, e = 1.602 × 10⁻¹⁹ C.
2. Mass of an electron, m = 9.0 × 10⁻³¹ kg.
3. Radius of an electron, r = 1.9 × 10⁻¹⁵ m.
5. Those substances whose atoms have their outermost orbit incomplete act as :
(a) good conductors of electricity
(b) insulators
(c) semiconductors
(d) any of the above
Solution:- (a)
A substance having large numbers of free electrons at room temperature is termed as conductor of electricity. Example:- Copper, aluminium, silver, gold, etc. When a potential difference is applied across a conductor material, free electrons immediately flow through the conductor material resulting in electric current.
6. The property of the electric circuit which opposes the flow of current is called:
(a) resistivity (b) resistance
(c) conductance. (d) conductivity.
Solution:- (b)
A substance that opposes the flow of current through through conductor is known as resistance. The familiar equation for resistance is it is represented as R and measured in ohm (Ω).
R = ρl / a .................Ohm (Ω)
Where,
R = resistance of the conductor.
ρ = resistivity of the material.
l = the length of the conductor.
a = cross - sectional area of conductor.
7. The unit of conductivity is:
(a) Ω (b) Ʊ/m (c) Ω/m (d) m/Ω
Solution:-(b)
Conductivity is the reciprocal of resistivity of the conductor. It is denoted by greek letter sigma 'σ'.
Conductivity = 1 / ρ
Since, G = 1 / R = a / ρl = σa / l. Hence, the SI unit of conductivity is Siemens/m or Ʊ/m.
8. How much work will be done by an electric energy source with a potential difference of 3 kV that delivers a current of 1 A for 1 minute ?
(a) 180 KJ (b) 108 KJ (c) 18 KJ (d) 80 KJ
Solution:-
Let, if 1 A of current represents a charge transfer rate of 1 C/s. Hence, the total charge for a period of 1 minute is;
Q = It = 1 × 60 = 60 C.
Total work done, W = Q × V
= 60 × (3 × 10³)
= 180 × 10³ J
= 180 kJ...Ans
9. The resistivity of insulators ........... rapidly with the rise of temperature.
(a) increases
(b) decreases
(c) first increases then decreases
(d) can't be determined
Solution:- (b)
Insulatos possess negative temperature coefficient of resistance, therefore their resistivity decreases with rise in temperature.
10. The insulation resistanceof cable varies .......... as the length.
(a) directly (b) indirectly
(c) three times (d) (a) and (b)
Solution:-(b)
Rᵢ = (ρ/ 2πl) × logₑ (r₂ / r₁)
r₂ = r₁+insulation thickness
r₁ = radius of core.
Thus, from above equation it is evident that insulation resistance Rᵢ inversely proportional to the length.
11. Kirchhoff’s current law states that
(a) net current flow at the junction is
positive
(b) algebraic sum of the currents
meeting at the junction is zero
(c) no current can leave the junction
without some current entering it.
(d) total sum of currents meeting at the
junction is zero.
Solution:-(b)
Kirchhoff's current law, states that the algebraic sum of the currents entering at a junction in an electric circuit is equal to zero.
12. According to Kirchhoff’s voltage law, the algebraic sum of all IR drops and e.m.f. in any closed loop of a network is always
(a) negative
(b) positive
(c) determined by battery e.m.fs
(d) zero.
Solution:-(d)
Kirchhoff's voltage law, states that in any closed electrical circuit or mesh, the algebraic sum of all the e.m.f and voltage drops across the resistor is equal to zero.
13. Kirchhoff’s current law is applicable to
only
(a) junction in a network
(b) closed loops in a network
(c) electric circuits
(d) electronic circuits.
Solution:-(a)
14. Kirchhoff’s voltage law is related to
(a) junction voltages
(b) battery e.m.fs
(c) IR drops
(d) both (a) and (b)
Solution:-(d)