Physics Test

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Physics Test - 23

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Question 1
1 / -0

A smooth sphere is moving on horizontal surface with a velocity vector $(2 \hat{i} + 2 \hat{j})$ m/s immediately before it hits a vertical wall. The wall is parallel to vectorand coefficient of restitution between the sphere (in m/s) and the wall is e = 1/2. The velocity of the sphere after it hits the wall is -

A
+2

B
-+2

C
-2

D
2-

Solution
Question 2
1 / -0

If $n_{R}$ and $n_{V}$ denote the number of photons emitted by a red bulb and violet bulb of equal power in a given time, then

A
$n_{R}=n_{V}$

B
$n_{R}>n_{V}$

C
b

D
d

Solution

Energy possessed by a photon is given by
$E = h f = \frac{h c}{λ}$
If power of each bulb is Pthen energy given out in time tequal to Pt.Let the number of photons be n, then
$n = \frac{P t}{E} = \frac{P t}{(h c / λ)} = \frac{P t λ}{h c}$
For red light, $n_{R} = \frac{P t λ_{R}}{h c}$
For violet light, $n_{V} = \frac{P t λ_{V}}{h c}$
$∴ \frac{n_{R}}{n_{V}} = \frac{λ_{R}}{λ_{V}}$
As $λ_{R} > λ_{V}$
So, nR>nV
Main Concept :
Intensity Of LightThe luminous intensity of a light source is the power of light. It is defined in a given direction and is measured in candela, cd. The candela is one of the seven base units of the SI system and specifies the luminous intensity in one specific angle from a light source. But it doesn’t indicate anything about the total amount of light being radiated from the light source. The scientific definition of the candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency $540 \times 10^{12}$ Hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
Question 3
1 / -0

A lead bullet strikes at target with a velocity of $480 \mathrm{m} \mathrm{s}^{-1}$. If the bullet falls dead, the rise in temperature of bullet $(c$ $\left.=0.03 \mathrm{cal} / \mathrm{g} /^{\circ} \mathrm{C}\right),$ assuming that heat produced is equally shared between the bullet and target is

A
c

B
b

C
a

D
d

Solution
Question 4
1 / -0

Which logic gate is represented by the following logic gates?

A
NOR

B
NAND

C
AND

D
OR

Solution

Truth table
This belongs to AND gate

A B Y

0 0 0

0 1 0

1 0 0

1 1 1

(OR)
b
Main Concept :
Truth table Of OR gate

A B A OR B

0 0 0

0 1 1

1 0 1

1 1 1

Other Concepts :
Concept 1 :
OR gate The OR gate is a digital logic gate that implements logical disjunction - it behaves according to the truth table to the right. A HIGH output (1) results if one or both the inputs to the gate are HIGH (1). If neither input is high, a LOW output (0) results. In another sense, the function of OR effectively finds the maximum between two binary digits, just as the complementary AND function finds the minimum.

Input Output

A B A OR B

0 0 0

0 1 1

1 0 1

1 1 1

Concept 2 :

These gates form the basis of modern communication through signals as signals get transferred in form of high voltage and low voltage i.e 1 and 0.

Gates are based on semiconductors which is further based on concept of forward biasing and reverse biasing.
Question 5
1 / -0

In a medium, the force of attraction between two point charges, which are at distance $d$ apart, is $F$. What distance apart should

these point charges be kept in the same medium, so that the force between them becomes $16 F ?$

A
$\frac{d}{2}$

B
$\frac{d}{4}$

C
$\frac{d}{\sqrt{3}}$

D
$\frac{d}{\sqrt{2}}$

Solution
Question 6
1 / -0

If the forward voltage in a diode is increased, the width of the depletion region :

A
Increases

B
Decreases

C
Fluctuates

D
No change

Solution

On increasing the forward bias voltage, the barrier energy decreases. This results in the flow of majority charge carries. Hence, width of depletion region decreases
Question 7
1 / -0

A nucleus is bombarded with a high speed neutron so that resulting nucleus is a radioactive one. This phenomenon is called

A
Artificial radioactivity

B
Fusion

C
Fission

D
Radioactivity

Solution

When atoms of an element are bombarded by neutrons, the atomic nuclei are (artificially) disintegrated and emit lighter particle (eg. $α - p a r t i c l e, β - p a r t i c l e$ ,proton etc.).

Sometimes a neutron is observed by the nucleus which is converted into its heavier isotope and energy is emitted in the form ofγ-photons.

This process in which heavy nucleus is broken into two nearly equal fragments is called nuclear fission.
Question 8
1 / -0

Typical silt(hard mud) particle of radius $20 μ m$ is on the top of lake water, its density is $2000 k g m^{- 3}$ and the viscosity of lake water is 1.0 mPa, density is $1000 k g m^{- 3}$ . If the lake is still(has no internal fluid motion). The terminal speed with which the particle hits the bottom of the lake is .......... ${m m s}^{- 1}$

A
0.67

B
0.77

C
0.87

D
0.97

Solution
Question 9
1 / -0

In an AC circuit the instantaneous values of emf and current are $e=200 \sin 300 t$ volt and $i=2 \sin \left(300 t+\frac{\pi}{3}\right)$ amp. The average power consumed in watt is

A
200

B
100

C
50

D
400

Solution
Question 10
1 / -0

A galvanometer of resistance $50 Ω$ is converted into ammeter by connecting a low resistance (shunt) of value $1 Ω$ in parallel to the galvanometer S. If full scale deflection current of galvanometer is 10 mA, then the maximum current to be measured by the ammeter is

A
500 mA

B
510 mA

C
610 mA

D
490 mA

Solution