Physics Test 279

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Physics Test 279

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Weekly Quiz Competition

Question 1
4 / -1

The energy required to remove the electron from a singly ionized Helium atom is 2.2 times the energy required to remove an electron from Helium atom. The total energy required to ionize the Helium atom completely is:

A
34 eV

B
20 eV

C
79 eV

D
109 eV

Solution

Option C is correct; the total energy required is 79 eV.

Let the first ionization energy be E₁ and the second ionization energy be E₂. Given E₂ = 2.2 E₁.

For the singly ionized helium ion (He⁺), which is hydrogen-like with atomic number Z = 2, the ionization energy from the ground state is given by 13.6 Z² eV.

Thus E₂ = 13.6 × 2² = 13.6 × 4 = 54.4 eV.

So E₁ = E₂ / 2.2 = 54.4 / 2.2 ≈ 24.73 eV.

Total energy to ionize helium completely = E₁ + E₂ = 24.73 + 54.4 ≈ 79.13 eV, which rounds to 79 eV.

Therefore the correct option is C: 79 eV.
Question 2
4 / -1

A solid sphere of mass 2 kg is resting inside a cube as shown in figure The cube is moving with a velocity Here t is time in seconds. All surfaces are smooth. The sphere is at rest with respect to the cube. What is the total force exerted by the sphere on the cube?

A
24 N

B
25 N

C
26 N

D
27 N

Solution

Option C is correct.

Differentiate the given velocity with respect to time to get the acceleration; a = (5 i + 2 j) m s^-2.

By Newton's second law the vector sum of external forces on the sphere equals m a.

Taking rightward as x and upward as y, the external forces are Nx i from the left wall, Ny j from the floor (upward), and weight mg (downward). Thus Nx i + (Ny - mg) j = m a.

With m = 2 kg, m a = (10 i + 4 j) N.

Equating components gives Nx = 10 N and Ny - mg = 4 N.

Using g = 10 m s^-2 (consistent with the options), Ny = 4 + m g = 4 + 2 × 10 = 24 N.

The resultant force magnitude is √(10² + 24²) = 26 N.

Hence the total force exerted by the sphere on the cube is 26 N (option C).
Question 3
4 / -1

A block is resting on a piston which executes simple harmonic motion in vertical plane with a period of 2.0 s in vertical plane at an amplitude just sufficient for the block to separate from the piston. The maximum velocity of the piston is

A
5/π m/s

B
10/π m/s

C
π/2 m/s

D
20/π m/s

Solution

The situation when the block is just below the mean position is shown in Fig., the restoring forces acting on the piston cause a normal reaction F to act on the block. For the block to separate F ≥ mg i.e., mω²A ≥ mg
Question 4
4 / -1

Determine the electric field intensity at point P due to quadruple distribution shown in figure for r ≫ a

A
0

B
kqa²/r⁴

C
6kqa²/r⁴

D
6kqa²/r²

Solution
Question 5
4 / -1

Two capacitors of capacitances 0.3μF and 0.6μF are connected in series across 6 volts. The ratio of energies stored in them will be

A
2:1

B
1:2

C
2:3

D
4:1

Solution
Question 6
4 / -1

Two coherent sources of intensity ratio 100 : 1, interfere. What is the ratio of the intensity between the maxima and minima in the interference pattern?

A
10 : 1

B
5 : 2

C
121 : 81

D
11 : 9

Solution
Question 7
4 / -1

A block of pure silicon at 300 K has a length of 10 cm and an area of 1.0 × 10⁻⁴ m². If a battery of emf 2 V is connected across it, what is the electron current? The mobility of electrons is 0.14 m² V⁻¹ s⁻¹ and their number density is 1.5 × 10¹⁶ m⁻³.

A
6.72 × 10⁻⁴A

B
6.72 × 10⁻⁵ A

C
6.72 × 10⁻⁶A

D
6.72 × 10⁻⁷ A

Solution
Question 8
4 / -1

Assertion: The speed of sound in a gas is not affected by change in pressure provided the temperature of the gas remains constant.

Reason: The speed of sound is inversely proportional to the square root of the density of the gas.

A
If both assertion and reason are true and reason is the correct explanation of assertion.

B
If both assertion and reason are true but reason is not the correct explanation of assertion

C
If assertion is true but reason is false.

D
If both assertion and reason are false.

Solution

Assertion and Reason are both correct and reason is not the correct explanation of assertion.

“At constant T, P and ρ change proportionally, keeping v constant.”
Question 9
4 / -1

Directions For Questions

Two identical blocks A and B are placed on two inclined planes as shown in diagram. Neglect air resistance and other friction

...view full instructions

Read the following statements and choose the correct options.

Statements I : Kinetic energy of 'A' on sliding to J will be greater than the kinetic energy of B on falling to M.

Statements II : Acceleration of ' A ' will be greater than acceleration of ' B ' when both are released to slide on inclined plane

Statements III : Work done by external agent to move block slowly from position B to O is negative

A
only statement I is true

B
only statement II is true

C
only I and III are true

D
only II and III are true

Solution

Statement I : Work done by gravity is same for motion from A to J and B to M for equal mass. So K.E. will be equal.
Question 10
4 / -1

The length, breadth and thickness of a rectangular sheet of metal are 4.234 m, 1.005 m, and 2.01 cm respectively. Give the volume of the sheet to correct significant figures.

A
0.0755 m³

B
0.1855 m³

C
0.0855 m³

D
0.08552 m³

Solution

Length , l = 4,234 m

Breadth, b = 1.005 m

Thickness , t = 2.01 x 10^-2 m

Volume = l x b x t

⇒ V = 4.234 x 1.005 x 0.0201 = 0.0855289 = 0.0855 m³ (significant figure = 3)