# Materials And Components MCQs

• A. 2.5 mH
• B. 5 mH
• C. 20 mH
• D. 40 mH

## A capacitor can be represented by a capacitance and resistance in parallel. For a good capacitor, this parallel resistance should be

• A. negligible
• B. low
• C. high
• D. very high

## A circular sphere mile is the area of cross-section of a wire

• A. having a diameter equal to 1 miles
• B. having a radius equal to 1 miles
• C. having a circumference equal to 1 miles
• D. none of the above

## A conductor carries 10 A current in + x direction and is lying in a field having a flux density 0.2 T directed along + z direction. The magnitude of force per metre length and direction are

• A. 2 N, + y direction
• B. 2 N, - y direction
• C. 0.02 N, + y direction
• D. 0.02 N, - y direction

• B. + 1
• C. - 1
• D. + 2

## A copper specimen has resistivity equal to 1.8 x 10-8 ohm-m at room temperature. At a temperature of 700 K, the resistivity is likely to be

• A. 1.6 x 10-8 Ω-m
• B. 2 x 10-8 Ω-m
• C. 3 x 10-8 Ω-m
• D. 6 x 10-8 Ω-m

## A dielectric is subjected to alternating field. The dielectric losses are potential to

• A. real part of dielectric constant
• B. imaginary part of dielectric constant
• C. both real and imaginary parts of dielectric constant
• D. either real or imaginary part of dielectric constant

## A dielectric material must be

• A. insulator
• B. good conductor
• C. resistor
• D. semiconductor

## A dielectric of relative permittivity ∈r is subjected to a homogeneous electric field E. The dipole moment P per unit volume is given by

• A. P = constant
• B. P = ∈0 E
• C. P = ∈0(∈r - 1) E
• D. P = ∈r E

## A good dielectric should have

• A. low losses
• B. good heat conductivity
• C. high intrinsic strength
• D. all of the above

## A liquid has N permanent dipoles μp per unit volume and has been subjected to dc field for a long time such that orientation polarization is P0. At t = 0, the field is suddenly removed, then polarization

• A. will remain constant at P0
• B. will become zero at t = 0
• C. will delay to zero with a time constant
• D. either b or c

## A magnet does not attract

• A. nickel
• B. iron
• C. copper
• D. iron and copper

## A magnetic field exists around

• A. moving charges
• B. static charges
• C. iron
• D. copper

## A material which is lightly repelled by a magnetic field is known as

• A. diamagnetic material
• B. non-magnetic material
• C. ferromagnetic material
• D. paramagnetic material

• A. 10-8 W
• B. 10-6 W
• C. 10-4 W
• D. 10-2 W

## A permeable substance is one

• A. which is strong magnet
• B. which is a weak magnet
• C. which is a good conductor
• D. through which magnetic lines of force can pass easily

## A photoconductor is a

• A. conductor
• B. semiconductor
• C. insulator
• D. superconductor

## A piece of copper and another piece of Germanium are cooled from 30°C to 80 K. The resistance of

• A. copper decreases and germanium increases
• B. both decreases
• C. both increases
• D. copper increases and germanium decreases

## A piece of iron is placed in a magnetic field

• A. the magnetic field will not be affected
• B. the magnetic lines of force will bend to pass through the piece
• C. the magnetic lines of force will bend away from the piece
• D. any of the above depending on type of iron

## A rare gas has N atoms per m3. If electronic polarizability of single atom of this gas is ae, then

• A. ∈r = Ne
• B. ∈0∈r = Ne
• C. ∈0(∈r - 1) = Ne
• D. ∈0(∈r - 2) = Ne

## A sample of N type semiconductor has an electron density of 6.25 x 1018/cm3 at 300 K. If intrinsic concentration of carriers in this sample is 2.5 x 1013/cm3 at this temperature, the hole density is

• A. 106 / cm3
• B. 108 / cm3
• C. 1010 / cm3
• D. 1012 / cm3

## A sheet of bakelite is inserted between the plates of an air capacitor. The capacitance will

• A. increase
• B. decrease
• C. remain the same
• D. may increase or decrease

• A. 0.5 L
• B. L
• C. 2 L
• D. 4 L

## A wire is carrying current I. The field intensity H at a distance r from the wire

• A. is directed towards wire
• B. is directed away from wire
• C. is tangential every where to a circle of radius r
• D. none of the above

## Above a certain temperature, the specific heat of a metal becomes constant. This temperature is called

• A. Debye temperature
• B. Curie temperature
• C. Neel temperature
• D. Transition temperature

## An atom of a rare gas is placed is an electric field E. Then

• A. the nucleus will be shifted in the direction of E by an amount which is proportional to E.
• B. the nucleus will not be shifted.
• C. the nucleus will be shifted in the direction of E by an amount which is independent of E.
• D. the nucleus will be shifted in a direction opposite to that of E.

## An electrolytic capacitor can be used for

• A. ac only
• B. dc only
• C. both ac and dc
• D. high frequency ac

• A. 0.5 eω R2
• B. eω R2
• C. 2 eω R2
• D. 0.5 eω R3

## An electron in a homogeneous magnetic field and having velocity perpendicular to the direction of field moves

• A. perpendicular to the field
• B. along the field
• C. along a straight line inclined at 45° to field
• D. in a circular path

## An electron shell corresponding to principal quantum number n can contain a maximum of

• A. n2 electrons
• B. 2n2 electrons
• C. 2n electron
• D. n3 electron

## An iron specimen has µr = 1000 when B = 0.3 T. If B = 0.35 T, µr

• A. will be 1000
• B. will be less than 1000
• C. will be more than 1000
• D. may be more or less than 1000

• A. aT = 0
• B. aT > i
• C. aT ∼ i
• D. aT < i

• A. 7
• B. 6
• C. 8
• D. 5

## As regards ∈0 and ∈r (absolute and relative permittivity)

• A. both ∈0 and ∈r can be interpreted in terms of atomic properties of medium
• B. only ∈r can be interpreted in terms of atomic properties of medium
• C. only ∈0 can be interpreted in terms of atomic properties
• D. ∈r has no physical significance

## As regards dielectric constant εr

• A. the units are farads/m
• B. the units are newton/coulomb
• C. it is dimensionless
• D. the units are farads

## As regards ferromagnetic Curie temperature Qf and paramagnetic curie temperature θ

• A. Qf > θ
• B. θ > Qf
• C. θ equal to or less than Qf
• D. θ may be equal to less than or more Qf

## As the atoms of rare gases become larger, electronic polarizability

• A. increases
• B. decreases
• C. remains the same
• D. may increase or decrease

## As the temperature of a pure silicon specimen is increased

• A. the number of free electrons increases
• B. the number of holes decreases
• C. the number of holes increases
• D. the number of free electrons and holes increases

## As the temperature of semiconductor is increased

• A. the average number of free charge carriers decreases
• B. the average number of free charge carriers increases
• C. the average number of free charge carriers remains the same
• D. the average number of free charge carriers may increase or decrease