SSC JE 2015 Electrical question paper with solution

In electrical engineering, the node refers to any point or junction on a circuit where two or more circuit elements meet.

The material used for the Core in a transformer is selected on the basis of its magnetic permeability and its characteristic hysteresis loop. A material with a low hysteresis loop area and high permeability need to be selected for the higher efficiency of the transformer.

Steel, silicon alloys have a very narrow hysteresis loop. Silicon steel alloy has high permeability and low hysteresis losses, therefore, these materials are used for transformer core and armature core which are subjected to rapid reversal of magnetization.

percent error = [experimental value – theoretical value] / theoretical value x 100%

75 -150 = -75

|-75| = 75

%error = 75/150

= 0.5%

The reluctance of a uniform magnetic circuit can be calculated as:

R = l/μo μr A

R ∝ 1/μo μr

Where l = length

μo = permeability of vacuum, equal to 4π × 10⁻⁷ 

μr  =  relative magnetic permeability of the material

A =  cross-sectional area of the circuit

Reluctance of air > Reluctance of iron

So air has the lowest relative permeability

The SI unit of luminous flux is the lumen (lm). One lumen is defined as the luminous flux of light produced by a light source that emits one candela of luminous intensity over a solid angle of one steradian.

The CE (common Emitter ) configuration is the only configuration that provides both voltage gain and current gain greater than unity.

In the case of CB (common Base) current gain is less than unity and in the case of CC (common collector) voltage gain is less than unity.

• The damage caused by electric shock depends on the current flowing through the body — 1 mA can be felt; 5 mA is painful.
• Above 15 mA, a person loses muscle control, and 70 mA can be fatal.”
• The amount of damage done by the electric shock depends not only on the magnitude of the current but also on which portions of the body that the electric current is flowing through. The reason for this is that different parts of the body have different resistances, which can lead to an increase in the current

In single-phase motors, there is only one main winding and a single-phase supply. So there is no RMF (rotating magnetic flux) generated inside the stator of such machines. So such machines are not inherently self-starting.

The auxiliary winding or starting winding is connected to the ac mains via a capacitor in order to generate a two-phase supply, which can generate RMF when the coils are spatially placed at 90° with respect to the main winding. This RMF is responsible for the operation of single-phase induction motors. Adding the capacitor makes the motor self-starting.