Physics Test 200

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Physics Test 200

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Weekly Quiz Competition

Question 1
4 / -1

Photons of energy 1eV and 2.5 eV successively illuminate a metal whose work function is 0. 5 eV. The ratio of the maximum speeds of the electrons emitted will be

A
1 : 4

B
1 : 2

C
2 : 1

D
4 : 1

Solution

Work function=0.5

for 1ev photon

1ev=0.5+kinetic energy

k.E=0.5ev

for 2.5ev photon

2.5ev=0.5ev+k.E

k.E=2ev

ratio of above2 k.E give ratio of square of velocity =1:4

taking square root

finelly the ratio of velocity =1:2ans
Question 2
4 / -1

When a charged oil drop moves upwards in an electric field, the electric force acting on the drop is

A
Equal to the gravitational force

B
Less than the garvitational force

C
Greater than the mass of the oil drop

D
Greater than the gravitational force
Question 3
4 / -1

The material which practically does not show elastic after effect is

A
Copper

B
Rubber

C
Steel

D
Quartz

Solution

When an elastic body is stretched and applied deforming force is removed then the body is expected to return to its original configuration instantaneously. This elastic after effect is very short for quartz fiber. But elastic after effect is more for glass.
Question 4
4 / -1

The average power dissipation in a pure capacitor in AC circuit is

A
1/2 CV²

B
CV²

C
2 CV²

D
Zero

Solution

Why Power in pure Capacitive Circuit is Zero (0)

Pure inductive circuit, current is lagging by 90 degree from voltage ( in other words, Voltage is leading 90 Degree from current) i.e the pahse difference between current and voltage is 90 degree.

So If Current and Voltage are 90 Degree Out of Phase, Then The Power (P) will be zero. The reason is that,

We know that Power in AC Circuit

P= V I Cos φ

if angle between current and Voltage are 90 ( φ = 90) Degree. then

Power P = V I Cos ( 90) = 0

[ Note that Cos (90) = 0]So if you put Cos 90 = 0→Then Power will be Zero (In pure Inductive circuit)
Question 5
4 / -1

A boat crosses a river from port A to port B, which are just on the opposite side. The speed of the water is vW and that of boat is vB relative to water. Assume vB = 2vW. What is the time taken by the boat, if it has to cross the river directly on the AB line?

A

B

C

D

Solution

Let the velocity of the boat, if it has to cross the river directly on water the line AB be v and the angle between and vB be θ. Then, from the figure sinθ=vwvB Given, vB=2vw ∴ sinθ=vw2vw=12 ⇒ θ=30o Now, the time is taken by the boat to cross the river directly from A to B t=DvA=DvBcosθ =DvBxcos30o or t=2DvB√ 3
Question 6
4 / -1

The root mean square velocity of the molecules in a sample of helium is 5/7th that of the moelcules in a sample of hydrogen. If the temperature of hydrogen sample is 0^oC, then the temperature of the helium sample is about

A
0^oC

B
0 K

C
273^oC

D
100^oC
Question 7
4 / -1

The electric potential at a point (x, y) in the xy-plane is given by: V = -kxy. The electric field intensity at a distance r from the origin varies as

A
r

B
2r

C
r²

D
2r²
Question 8
4 / -1

A student has measured the length of a wire equal to 0.04580 m. This value of length has the number of significant figures equal to

A
five

B
four

C
six

D
None of these

Solution

Zero on right having decimal place are counted. For a number less than 1, zeroes on left of first non zero-digit are not significant

The number of significant figures in 0.04580 is 4
Question 9
4 / -1

The capacity of a parallel plate condenser is 10 μ Fd without dielectric. After that, a dielectric of constant 2 is used to fill half thickness between the plates of another capacitor of same capacitance. The net capacitance after joining both of them in series in μ Fd is

A
10

B
20

C
15

D
13.33

Solution

Initial c = 10

let capacitance of capictor with dielectric is C1 and without dielectric is ç2

finally they are connected in series

therefore Ceq= C1*C2/(C1+C2)

C1=2*10*2=40

C2=10*2=20

Hence Ceq = 40*20/(20+40)

800/60

=13.33.
Question 10
4 / -1

If the earth is at one-fourth of its present distance from the sun, then duration of the year will be

A
half of the present year

B
one-fourth of the present year

C
one -sixth of the present year

D
one-eighth of the present year

Solution

BY Keplers's 3rd law......

Time period T^2=kR^3.

where R is distance of the earth from sun..

so if R'=R/4

T'²=KR'³

T'²=KR³/64

T'²=T²/64

T'=T/8

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Physics Test 200

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Physics Test 200

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SHARING IS CARING

Question 1

1 : 4

1 : 2

2 : 1

4 : 1

Solution

Question 2

Equal to the gravitational force

Less than the garvitational force

Greater than the mass of the oil drop

Greater than the gravitational force

Question 3

Copper

Rubber

Steel

Quartz

Solution

Question 4

1/2 CV2

CV2

2 CV2

Zero

Solution

Question 5

Solution

Question 6

0oC

0 K

273oC

100oC

Question 7

r

2r

r2

2r2

Question 8

five

four

six

None of these

Solution

Question 9

10

20

15

13.33

Solution

Question 10

half of the present year

one-fourth of the present year

one -sixth of the present year

one-eighth of the present year

Solution

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1/2 CV²

CV²

2 CV²

0^oC

273^oC

100^oC

r²

2r²