Exercise: Materials And Components

Questions for: Materials And Components

A metal has a large number of free electrons. If e is electronic charge and m is mass of electron and an electric field E is applied along (say) x direction, the electrons acquire a velocity having a component vx is x direction. Then
A:
B:
C:
D:
Answer: C
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Which of the following is used in temperature alarm circuits?
A:
Thermistor
B:
Photoconductor
C:
Transistor
D:
Varistor
Answer: A
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A specimen of metal has n valence electrons per m3. If vx is the average velocity of these electrons, each having a charge e, the current density J is
A:
J = ne vx
B:
J = - ne vx
C:
J =
D:
J =
Answer: B
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Assertion (A): In a conductor, current density remains constant in time as long as E is constant.

Reason (R): In a conductor, J = σE.

A:
Both A and R are true and R is correct explanation of A
B:
Both A and R are true but R is not correct explanation of A
C:
A is true but R is false
D:
A is false but R is true
Answer: A

In conductors constant E means constant current because conductivity is constant.

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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
Answer: B
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