Quiz: Electrical Engineering 12 Oct 2020

Quiz: Electrical Engineering
Exam: SSC-JE
Topic: Utilization of electrical energy

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. According to inverse square law illumination, what is the relation between illumination(E) and the distance between the light source and surface(d)?
(a) E ⍺ d
(b) E ⍺1/d
(c) E ⍺ d^2
(d) E ⍺1/d^2

Q2. According to lambert’s law, the illumination on a surface is proportional to
(a) cos⁡Ө
(b) cos^2⁡Ө
(c) 1/cos^2⁡Ө
(d) 1/cos^3⁡Ө

Q3. Direct lighting method of illumination is used in
(a) Houses
(b) Industries
(c) Outdoor lightning
(d) All of the above

Q4. In the indirect method of lighting about how much percentage of light falls on the surface?
(a) 10 %
(b) 50 %
(c) 75 %
(d) 90 %

Q5. Lumen/ watt is the unit of
(a) Light flux
(b) Luminous intensity
(c) Brightness
(d) Luminous efficiency

Q6. Luminous flux is
(a) Rate of energy radiation in the form of light waves
(b) Light energy radiated by sun
(c) Part of light energy radiated by sun which is received on earth
(d) None of the above

Q7. In dielectric heating current flows through
(a) Metallic conductor
(b) Air
(c) Dielectric medium
(d) Ionic discharge between dielectric medium and metallic conductor

Q8. In dielectric heating, if the capacitance is loss free, the heat produced will be
(a) Proportional to the value of capacitance
(b) Proportional to the frequency
(c) Infinity
(d) Zero

Q9. Plant capacity factor of a power plant may be calculated by the formula:
(a) (Average demand)/(Plant capacity)
(b) (Plant capacity)/(Average demand)
(c) (Sum of individual max. ⁡demand)/(Max demand of plant)
(d) (Station output)/(Plant Hours of use)

Q10. Demand factor of a power plant is:
(a) (maximum demand)/(connected load)
(b) (average demand)/(plant capacity)
(c) (station energy output)/(plant capacity×hrs of use)
(d) (average demand)/(maximum demand)

SOLUTIONS
S1. Ans.(d)
Sol. laws of illumination:
Illumination is directly proportional to the luminous intensity of the source.
Inverse square law – The illumination of a surface receiving its flux from a point source is inversely proportional to the square of the distance between the surface and the source.
i.e. E=I/d^2
where, E=illumination
I= intensity
d =distance

S2. Ans.(a)
Sol. laws of illumination:
Illumination is directly proportional to the luminous intensity of the source.
Inverse square law – The illumination of a surface receiving its flux from a point source is inversely proportional to the square of the distance between the surface and the source.
Lambert’s cosine law – The illumination of a surface at any point is proportional to the cosine of the angle between the normal at the point and the direction of the luminous flux.
i.e. E ⍺1/(d^2 )⍺1/d^2 cos⁡Ө
Illumination(E)=I/d^2 cos⁡Ө
where, E=illumination
I= intensity
d =distance

S3. Ans.(d)
Sol. In direct lighting method of lighting, an opaque reflector directs 90 % of the light vertically downwards. Only 10 % of light will be absorbed in this system by the reflector. It is uses in houses, industries and general outdoor lighting.

S4. Ans.(a)
Sol. indirect lighting method of lighting, 90 % of the light is reflected upwards and only 10 % falls on the surface. They are used for mainly decoration purposes in cinemas, hotels, club etc.

S5. Ans.(d)
Sol. Luminous efficiency is the ratio of the total luminous flux radiated by any source to the total radiant flux from the source commonly expressed in lumens per watt.

S6. Ans.(a)
Sol. Luminous flux is the measure of brightness of a light source in terms of energy being emitted. Luminous flux, in SI units, is measured in the lumen (lm). It is a measurement of energy released in the form of visible light from a light-producing source.

S7. Ans.(c)
Sol. In dielectric heating current flows through dielectric materials. The dielectric acts as capacitance.

S8. Ans.(d)
Sol. Dielectric loss(P)=2πfCV^2 cos⁡Ө
For loss free capacitor, Ө=90⁰⇒P=0
Hence, heat produced will be zero.

S9. Ans.(a)
Sol. (plant capacity factor=(peak load)/(plant capacity)×load factor)
=(Average demand)/(Plant capacity)

NOTE: If peak load equals to plant capacity then load factor = capacity factor.

S10. Ans.(a)
Sol. Demand factor = (Maximum demand)/(connected load)
Demand factor is less than 1.

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