In semiconductors at a room temperature

the conduction band is completely empty
the valence band is partially empty and the conduction band is partially filled
the valence band is completely filled and the conduction band is partially filled
the valence band is completely filled

Solution

In semiconductors, the conduction band is empty and the valence band is completely filled at 0 K.No electron from valence band can cross over to conduction band at 0 K.But at room temperature some electrons in the valence band jump over to the conduction band due to the small forbidden gap, i.e.,1 eV.

The vector sum of two forces is perpendicular to their vector differences. In that case, the forces

cannot be predicted
are equal to each other
are equal to each other in magnitude
are not equal to each other in magnitude

Solution

Illuminance of a surface is measured in

Lumen
candela
lux
lux m^-2

Solution

Illuminance is intensity of illumination measured in lux.

The figure shows a logic circuit with two inputs A and B and the output C. The voltage wave forms across A, B and C are as given. The logic gate circuit is:

OR gate
NOR gate
AND gate
NAND gate

Solution

If a bar is made of copper whose coefficient of linear expansion is one and a half times that of iron, the ratio of force developed in the copper bar to the iron bar of identical lengths and cross-sections, when heated through the same temperature range (Young’s modulus of copper may betaken to be equal to that of iron) is

Solution

F=Y α t A or F∝a
(∵Y t A is same for both copper and iron)
or F_C ∝ α_C and F₁∝ α₁
\(∴\frac{F_{C}}{F_{1}}=\frac{3/2}{1}=\frac{3}{2}\)

For adiabatic processes (Letters have usual meanings)

P^γV = constant
T^γV = constant
TV^γ–1= constant
TV^γ= constant

A torch bulb rated as 4.5 W, 1.5 V is connected as shown in fig. The e.m.f. of the cell, needed to make the bulb glow at full intensity is

4.5 V
1.5 V
2.67 V
13.5 V

Solution

When the light is incident at the polarizing angle on the transparent medium, then the completely polarized light is

refracted light
reflected light
refracted and reflected light
neither reflected nor refracted light

Solution

When the light is incident at the polarising angle on the transparent medium, the reflected light is completely polarised.

The third line of Balmer series of an ion equivalnet to hydrogen atom has wavelength of 108.5 nm. The ground state energy of an electron of this ion will be

3.4 eV
13.6 eV
54.4 eV
122.4 eV

Solution

A bus starts moving with acceleration 2 m/s². A cyclist 96 m behind the bus starts simultaneously towards the bus at 20 m/s. After what time will he be able to overtake the bus?

4 sec
8 sec
12 sec
16 sec

Solution

Which of the following must be known in order to determine the power output of an automobile?

Final velocity and height
Mass and amount of work performed
Force exerted and distance of motion
Work performed and elapsed time of work

Solution

Power is defined as the rate of doing work.For the automobile, the power output is the amount of work done (overcoming friction)divided by the length of time in which the work was done.

The greatest height to which a man can through a ball is h.What is the greatest horizontal distance to which he can throw the ball?

2h
^h⁄₄
^h⁄₂
None of these

The electric field intensity just sufficient to balance the earth’s gravitational attraction on an electron will be: (given mass and charge of an electron respectively are 9.1 × 10 ^-31 kg and 1.6 × 10^-19C.)

–5.6 × 10^–11 N/C
–4.8 × 10^–15 N/C
–1.6 × 10^–19 N/C
–3.2 × 10^–19 N/C

Solution

A Second’s pendulum is placed in a space laboratory orbiting around the earth at a height 3 R from the earth’s surface where R is earth’s radius. The time period of the pendulum will be

zero
23
4 sec
infinite

Solution

The second pendulum placed in a space laboratory orbiting around the earth is in a weightlessness state.Hence g = 0 so T = ∞

By increasing the temperature, the specific resistance of a conductor and a semiconductor

increases for both
decreases for both
increases, decreases
decreases, increases

Solution

The resistivity of conductor increases with increase in temperature. The resistivity of semiconductor decreases as the temperature increases

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