SSC JE 2015 Electrical question paper with solution

Given

i = 2A

B = 1.4 wb/m²

N = 350

D = 12cm = 0.12 m

The magnetomotive force in ampere-turns can be expressed as:

F = NI

= 350 × 2 = 700 AT

Electrical resistivity, represented by ρ (rho), is a measure of how strongly a material opposes the flow of electric current. The lower the resistivity, the more readily the material permits the flow of electric charge.

The electrical resistivity of the copper is low as its conductivity is high whereas the electrical resistivity of the alloy is more

• SiO2 plays an important role in IC technology because It acts as a diffusion mask permitting selective diffusions into silicon wafers through the window etched into oxide and no other semiconductor material has a native oxide that is able to achieve all the properties of SiO₂.
• It acts as the active gate electrode in the MOS device structure.
• It provides electrical isolation of multilevel metallization used in VLSI.
• SiO₂ is used to isolate one device from another.

By using the fluorescent tube in DC operation the tube life is decreased by 80% due to the presence of ripple.

With an increase in the number of coils, the flux linkage in the coil is increased which increases the overall inductance of that coil.

Megohmmeters (also a trademarked device Megger) is used to measure large values of resistance.

Resistor values can be known by the color band.

0 black

1 blue

2 red

3 orange

4 yellow

5 green

6 blue

7 violet

8 grey

9 white

First color = digit
Second color=digit
Third color= power of ten
Fourth color =tolerance

In a resistor, the first color means the value first digit that is

Red – 2

Orange – 3

but that next on Orange means the power of 10

Orange – 10³

that color code silver means to withstand the power of the resistor +/- 10%.

We get the Resistance value from the color code (red, orange, orange, silver) is 23 (10³) = 23000.

Here we are not considering the last color (tolerance-silver) Because in the question there is no specification of minimum or maximum current.

So current I = V/R = 50/23000 = 0.00217 = 2.2mA.

We use universal motors in mixer grinders. Universal motors can run both on a.c. and d.c.These motors have high starting torque and speed, hence these are most preferred.

Ta vs Ia graph of DC series motor

In the case of the DC series, motor torque is proportional to the square of the armature current and this relation is parabolic in nature.

As load increases, armature current increases and torque produced increases proportional to the square of the armature current upto a certain limit.

After reaching the Saturation point though the current through the winding increases, the flux produced remains constant. Hence after saturation, the Ta Ia takes the shape of a straight line as flux becomes constant.

A transformer is said to be on “no-load” when its secondary side winding is open-circuited. When the transformer is in no-load condition there will be no current in the secondary section. The losses on the primary side are the core loss, dielectric loss and copper loss due to excitation current are the no-load losses and usually, they are pretty small which is about 2 – 5% of full load.