1.Which of the following is NOT an insulator?
SSC JE 20.10.2020, Shift-IExplain:- Insulators opposes the flow of current and make poor conductor. Some example of insulators are glass, plastic, rubber and wood etc.
Conductor conduct electrical current very easily because of their free electron. Some example of conductor are copper, aluminium, gold and silver.
2.Which of the following material has the least resistivity?
SSC JE 24.03.2021, Shift-IIExplain:- Aluminum is a good conductor of electricity, hence Aluminum has very low resistivity. Resistivity of aluminum is 2.8 ×10-8 Ω-m
3.Eureka is a commercial name of a heating element whose composition is:
SSC JE 24.03.2021, Shift-IIExplain:-
1. Eureka is a commercial name of heating element whose composition is 55% copper and 45% nickel.
2.Constantan is a nickel-copper alloy also known as Eureka.
3.Eureka is a nickel-copper based alloy wire that has resistivity and is mainly used for thermocouples and electrical resistance heating.
4.Polystyrene is an example of _____.
SSC JE 24.03.2021, Shift-IExplain:-
: Polystyrene is an example of insulator. Some other example of insulators are plastics, rubber, paper, glass etc.
Examples of super conductors are niobium, iron, prictides etc.
Examples of semiconductors are silicon, gallium arsenide, germanium etc.
Examples of conductors are copper, aluminium, gold etc. Dielectric constant polystyrene is 2.6 and also dielectric strength of polystyrene is 24×106V/m.
5.When the relative permeability of a material is slightly less than 1, it is called a
SSC JE 23, 24, 27.01.2018, Shift-II SSC JE 01.03.2017, Shift-IIExplain:-
6.Pure metals generally have............
SSC JE 04.03.2017, Shift-IIExplain:- Pure metals generally have high conductivity and large temperature coefficient. Pure metal has positive temperature co-efficient.
7.The trade name of Nickel-Copper alloy, that is used as a heating element is-
SSC JE 26.09.2019, Shift-IExplain:- Eureka is the trade name of Nickel-copper alloy. It consists of 60% copper and 40% Nickel. Its resistance temperature coefficient is low.
8.Which of the following is a diamagnetic material?
SSC JE 27.01.2018, Shift-IExplain:- : Lead is a chemical element with its symbol Pb. It's atomic number is 82. It is a heavy metal that is denser than most of the common materials. The relative permeability of paramagnetic material is greater than 1 and less than 1000. Lead is a diamagnetic material diamagnetic materials have µr less than 1.
{µr= relative permeability}
9.Which of the following material shows paramagnetism?
SSC JE 27.01.2018, Shift-IExplain:- Titanium is a paramagnetic material gets attract in the direction of magnetic field. the susceptibility of paramagnetic material is positive and very little. Their relative permeability is slightly greater than one (µr>1)
10.Which of the following materials has the least resistivity?
SSC JE 20.10.2020, Shift-I SSC JE 2012Explain:- The copper materials has the least resistivity.
Materials Resistivity
Silver – 1.6 × 10–8 Ωm
Iron – 9.7 × 10–8 Ωm
Carbon – 5.8 × 10–4 Ωm
Copper – 1.68×10–8 Ωm
11.Limiting temperature of F class insulating material :
SSC JE 2012Explain:-There are basically four classes of insulation A, B, F and H. Class F being the most commonly used. The limiting temperature of F class insulating material is 155 ºC.
These temperature ratings are -
Class A – 105º C
Class E – 120º C
Class B – 130º C
Class F – 155º C
Class H – 180 ºC
Class C – above 180 ºC
12.The magnetic materials that are used to prepare permanent magnets should have
SSC JE 2012Explain:- Properties of the material of a permanent magnet-
1.It should have high retentivity so, that it remains magnetised in the absence of the magnetising field.
2.It should have high saturation magnetisation.
3. should have high coercivity so that it does not get demagnetised easily.
13.Which type of insulation covering the conductor used for low voltage?
SSC JE 23.01.2018, Shift-IIExplain:- Cotton and Silk insulation covering the conductor used for low voltage.
The conductor may have a single layer or double layer covering depending upon the requirements of service. Silk or cotton covered wires are usually used for instrument and motor winding.
14.Absorbed moisture contents affect the dielectric strength ............
SSC JE 24.01.2018, Shift-I SSC JE 02.03.2017, Shift-IIExplain:- Dielectric strength is the maximum voltage that can be applied to a given material without causing it to break down. Usually expressed in kV/mm.
Dielectric strength is depends on various factors such as moisture content, temperature, thickness of a material. Absorbed moisture content affect the dielectric strength indirectly.
15.Oxygen is a/an…………gas?
SSC JE 26.09.2019, Shift-IIExplain:- Paramagnetic- Gaseous oxygen is paramagnetic also but it is moving too fast to be affected by the magnets. The reason that it is paramagnetic is because the oxygen molecule has two unpaired electrons. Unpaired electron, spin in the same direction as each other which increased the magnetic field effect.
16.Which of the following heating element has lowest operating temperature?
SSC JE 26.09.2019, Shift-IIExplain:- Eureka- Eureka has the lowest (450oC) operating temperature.
It biggest feature is that its resistivity remains almost constant of changing temperature. Eureka contains 60% copper and 40% Nickel. It is used in heaters and low temperature furnaces and stoves.
17.Which one of the following material does not have a constant relative permeability?
SSC JE 29.01.2018, Shift-IExplain:- The relative permeability of ferromagnetic material is much greater than 1. It does not have constant relative permeability. Permeability is reciprocal of magnetic reluctivity. Reluctivity is the measure of the resistance of a material against the formation of a magnetic field. otherwise known as distributed inductance in transmission line theory. It is denoted by µ.
18.Dielectric strength of rubber is around
SSC JE 22.01.2018, Shift-IIExplain:- Dielectric strength of rubber is around 30kV/mm. rubber is an insulating material, which is used in cable for insulation. Rubber, PVC, XLPE etc. are used for voltage below than 1kV, whereas paper is used for voltage above 1kV.
19.Material used for making electric plug is
SSC JE 29.01.2018 Shift-IIExplain:- Bakelite is used in making electrical switches and plugs. A plug consists of case or cover, three pins a fuse and a cable grip. The case of plug is the plastic or rubber parts that surround it. Plastic or rubber materials are used because they are good electric insulator.
20.Melting temperature of tungsten is
SSC JE 29.01.2018 Shift-IIExplain:-Tungsten or wolfram, is a chemical element with the symbol W and atomic number 74. The melting point of tungsten is 34,22°C (3422+273) =3695K and the boiling point is 5555°C. Tungsten is commonly used in heavy metal alloy such as high speed, from which cutting tools are manufactured.
21.Dielectric loss is proportional to
SSC JE 2014, Shift-IExplain:-
22.The relative permeability of paramagnetic material is …….
SSC JE 25.01.2018, Shift-II SSC JE 01.03.2017, Shift-IIExplain:-
23.A material which is slightly repelled by a magnetic field is known as..............
SSC JE 02.03.2017 Shift-IExplain:- Diamagnetic materials are slightly repelled by a magnetic-field and the material does not retain the magnetic properties when the external field is removed. In diamagnetic material all the electrons are paired so there is no permanent magnetic moment per atom.
Example- Copper, Zinc, Bismuth, Silver, Gold, Antimony, Marble, Water, Glass, NaCl etc
24.A magnet is able to attract____:
SSC JE 03.03.2017 Shift-IExplain:- A magnet is able to attract nickel, cobalt and steel. Therefore magnet is called permanent magnet.
99.At what temperature value is the insulation resistance corrected if it is measured to be different?
SSC JE 03.03.2017 Shift-IIExplain:- Insulation resistance is temperature sensitive. When temperature increases, insulation resistance decreases and vice-versa. At 22 ºC temperature, the insulation resistance corrected if it is measured to be different.
25.The material used for the magnetic circuit where high value of flux density required is ...........
SSC JE 01.03.2017, Shift-IIExplain:- The material used for the magnetic circuit where high value of flux density required is ferrocobalt or ferromagnetic core. The ferromagnetic material have a very high level of permeability.
26.Magnetic recording tape is most commonly made from............
SSC JE 01.03.2017, Shift-IIExplain:- Magnetic recording tape use a different type of hard magnetic material are iron oxide (ferric oxide), chromium dioxide, cobalt coated iron oxide or pure iron.
27.Following graph shows the loss characteristics of
a sheet of ferromagnetic material against
varying frequency f. Pi
, is the iron loss at
frequency f, Hysteresis and eddy current losses
of the sheet at 100 Hz are
Explain:-
