Physics Test 207

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Physics Test 207

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Weekly Quiz Competition

Question 1
4 / -1

If the potential difference of a 6µF capacitor is changed from 10V to 20V, the increase in energy stored will be

A
2×10^–4 J

B
3×10^–4 J

C
4×10^–4 J

D
9×10^–4 J

Solution
Question 2
4 / -1

In scattering, the impact parameter b is defined as the:

A
maximum kinetic energy of the scattering projectile

B
distance of closest approach between projectile and target

C
closest distance between projectile and target if there were no deflection

D
distance between projectile and target for which there is maximal deflection

Solution

The impact parameter is defined as the perpendicular distance between the path of a projectile and the center of a potential field created by an object that the projectile is approaching. It is often referred to in nuclear physics (see Rutherford scattering) and in classical mechanics.
Question 3
4 / -1

The photoelectric threshold frequency of a metal is f₀. When light of frequency 4f₀is incident on the metal, the maximum K.E. of the emitted electron is

A
2 hf₀

B
4 hf₀

C
3 hf₀

D
hf₀/ 2

Solution

The maximum kinetic energy of the emitted electrons is given by

K_max=hυ−ϕ₀=h(4υ)−h(υ)=3hυ
Question 4
4 / -1

The ionisation energy of hydrogen atom is 13.6eV, the ionisation energy of helium atom would be

A
13.6 eV

B
27.2 eV

C
6.8 eV

D
54.4 eV

Solution

E ∝ Z² and Z for helium = 2

∴ (E)_He = 4x13.6 = 54.4 eV
Question 5
4 / -1

Two point charges 10C and -10C are placed at a certain distance. What is the electric potential of their midpoint?

A
Some positive value

B
Some negative value

C
Zero

D
Depends on medium

Solution

Electric potential is a scalar quantity and its value is solely dependent on the charge near it and the distance from that charge. In this case, the point is equidistant from the two point charges and the point charges have the same value but opposite nature. Therefore equal but opposite potentials are generated due to the charges and hence the net potential at midpoint becomes zero.
Question 6
4 / -1

Photons of frequency f is incident on a metal surface of threshold frequency f₀. The maximum K.E. of emitted photoelectrons is

A
h(f + f₀)

B
hf₀

C
h(f – f₀)

D
hf

Solution

K_max=eV₀=hf-hf₀

K_max=eV₀= h(f-f₀)
Question 7
4 / -1

Point charges + 4q, –q and +4q are kept on theX-axis at points x = 0, x =a and x = 2a respectively.

A
Only – q is in stable equilibrium

B
None of the charges is in equilibrium

C
All the charges are in unstable equilibrium

D
All the charges are in stable equilibrium.

Solution

Net force on each of the charge due to the other charges is zero. However, disturbance in any direction other than along the line on which the charges lie, will not make the charges return.
Question 8
4 / -1

In the mass number range A = 30 to 170, the binding energy per nucleon is

A
decreases with increasing A

B
increases linearly with A

C
decreases linearly with A

D
nearly constant

Solution

The binding energy is a very short order range force.

So beyond a certain amount of range the force has no influence beyond that. that's why after certain number the binding energy per nucleon do not change even if we add more nucleons.
Question 9
4 / -1

The ratio of the speed of the electron in the ground state of hydrogen atom to the speed of light is

A
1/237

B
2/137

C
1/137

D
1/2

Solution

The speed of revolving electron in nth state of hydrogen atom is:

v=e²/2nhϵ₀

For n=1,

v= (1.6×10⁻¹⁹)²/2(1)(6.6×10⁻³⁴)(8.85×10⁻¹²)

v=2.56×10⁻³⁸/116.82×10⁻⁴⁶

v=0.0219×10⁸ms⁻¹

The speed of light is 3×10⁸

Hence,

v/c=0.0219×10⁸/3×10⁸

v/c=1/137
Question 10
4 / -1

If the internal resistance of a cell is 20 ohm and resistance of the circuit is also 20 ohm. Will the current remain same whether the given n identical cells are in series or in parallel?

A
yes

B
No

C
Can’t predict

D
None of the above

Solution

In series connection of cells total internal resistance=nr total resistance of circuit=nR current is same potential difference is different so,I=nv/nR+nr I=V/R+r current is same as before in parallel connection of cells total internal resistance=r/n total resistance of circuit=R/n total current=nI potential difference is same nI=V/r/n+R/n I=V/R+r current is same as before.

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Physics Test 207

Result

Physics Test 207

Score

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Rank

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Question 1

2×10–4 J

3×10–4 J

4×10–4 J

9×10–4 J

Solution

Question 2

maximum kinetic energy of the scattering projectile

distance of closest approach between projectile and target

closest distance between projectile and target if there were no deflection

distance between projectile and target for which there is maximal deflection

Solution

Question 3

2 hf0

4 hf0

3 hf0

hf0/ 2

Solution

Question 4

13.6 eV

27.2 eV

6.8 eV

54.4 eV

Solution

Question 5

Some positive value

Some negative value

Zero

Depends on medium

Solution

Question 6

h(f + f0)

hf0

h(f – f0)

hf

Solution

Question 7

Only – q is in stable equilibrium

None of the charges is in equilibrium

All the charges are in unstable equilibrium

All the charges are in stable equilibrium.

Solution

Question 8

decreases with increasing A

increases linearly with A

decreases linearly with A

nearly constant

Solution

Question 9

1/237

2/137

1/137

1/2

Solution

Question 10

yes

No

Can’t predict

None of the above

Solution

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2×10^–4 J

3×10^–4 J

4×10^–4 J

9×10^–4 J

2 hf₀

4 hf₀

3 hf₀

hf₀/ 2

h(f + f₀)

hf₀

h(f – f₀)