CBSE 11TH PHYSICS - Online Test

Q1. The order of inter atomic distance in liquids is about

A. 1000A∘

B. 100A∘

C. 2A∘

D. 20A∘

Answer : Option C
Explaination / Solution:

Using the assumption of little spheres (for interatomic space) the spacing between the molecules at about 2X10-10 m i.e. $2 A^{\circ}$

The size of an atom is about an angstrom (10 -10 m) . In solids, which are tightly packed, atoms are spaced about a few angstroms (2 Å) apart.

Thermal Properties of Matter Prepare / Learn

Q2. Plots of pressure as a function of temperature for gas thermometers containing different types and quantities of gas converge to the same point when extrapolated to zero pressure. The temperature value to which converge is.

A. 232.15

^{\circ}

B. 273.15

^{\circ}

C. 32.15

^{\circ}

D. -212.00

^{\circ}

Answer : Option B
Explaination / Solution:

Absolute zero temp. = 0K

Units and Measurements Prepare / Learn

Q3. Joule is the SI unit of

A. acceleration

B. power

C. force

D. work

Answer : Option D
Explaination / Solution:

The joule (symbol J), is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metre or N⋅m).

Oscillations Prepare / Learn

Q4. Any periodic function can be expressed as superposition of-

A. Sine and cosine functions of increasing intergral time period with suitable coefficients

B. Polynomial functions of different time periods with suitable coefficients

C. Any trigonometric functions of real time periods with suitable coefficients

D. Sine and Cosine functions of fixed time periods with suitable coefficients

Answer : Option D
Explaination / Solution:

Because sine and cosine functions both are periodic in nature and according to Fourier theorem a" Fourier series" is a way to represent a function as the sum of simple sine waves. More formally, it decomposes any periodic function or periodic signal into the sum of a (possibly infinite) set of simple oscillating functions, namely sines and cosines, or in simple terms any periodic function can be expressed as sum or superposition of sine and cosine functions with fixed time periods.

Gravitation Prepare / Learn

Q5. A ‘central’ force is always directed

A. at a fixed angle to the position vector of the point of application of the force with respect to the fixed point

B. along the position vector of the point of application of the force with respect to the fixed point

C. at a varying angle to the position vector of the point of application of the force with respect to the fixed point

D. perpendicular to the position vector of the point of application of the force with respect to the fixed point

Answer : Option B
Explaination / Solution:

The motion of a particle under a central force F always remains in the plane defined by its initial position and velocity.This may be seen by symmetry. Since the position r, velocity v and force F all lie in the same plane, there is never an acceleration perpendicular to that plane, because that would break the symmetry between "above" the plane and "below" the plane.

To demonstrate this mathematically, it suffices to show that the angular momentum of the particle is constant. This angular momentum L is defined by the equation

L = r \times p = r \times m v

Motion in A Straight Line Prepare / Learn

Q6. For one dimensional motion displacement is the

Δ x = (x_{2} + x_{1}) / 2

Δ x = (x_{2} + x_{1}) / 2

∆ x = 2 (x_{2} + x_{1})

B.

Δx=2(x2+x1)

change in position:

Δx=x2−x1

D. change in position:

Δ x = x_{2} + x_{1}

Answer : Option C
Explaination / Solution:

Displacement is defined to be the change in position of an object. It can be defined mathematically with the following equation:

$D i s p l a c e m e n t = ∆ x = x_{2} - x_{1}$

$x_{2}$ refers to the value of the final position.

$x_{1}$ $x_{1}$ refers to the value of the initial position.

$∆ x$ is the symbol used to represent displacement.

Waves Prepare / Learn

Q7. in longitudinal waves, the constituents of the medium

A. oscillate at 30

^{\circ}

to the direction of wave propagation

B. oscillate at 40

^{\circ}

to the direction of wave propagation

C. oscillate perpendicular to the direction of wave propagation

D. oscillate along the direction of wave propagation

Answer : Option D
Explaination / Solution:

In longitudinal wave motion, medium particles oscillates or vibrates in same direction of wave propagation to produce compression & rarefaction in wave propagation.

System of Particles and Rotational Motion Prepare / Learn

Q8. considering binary (double) stars in our frame of reference, the trajectories of the stars are a combination of

A. (i) uniform motion in a circle of the centre of mass and (ii) circular orbits of the stars about the centre of mass

B. (i) uniform motion in a straight line of the centre of mass and (ii) circular orbits of the stars about the centre of mass

C. i) uniform motion in a straight line of the centre of mass and (ii) elliptical orbits of the stars about the centre of mass

D. i) uniform motion in a straight line of the centre of mass and (ii) straight line motion of the stars about the centre of mass

Answer : Option B
Explaination / Solution:

A double star or visual double is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope.

In absence of external force Centre of mass of double star moves like a free particle. In Centre of mass frame both stars moving in a circle about the Centre of mass which is at rest and both star are diametrically opposite to each other.

Thus in our frame of reference, the trajectories of the stars are a combination of (i) uniform motion in a straight line of the Centre of mass and (ii) circular orbits of the stars about the Centre of mass.

Work Energy and Power Prepare / Learn

Q9. If F is a force and d is the displacement in the direction of force then the work done by the force is given by

A. - F.d

B. -2F.d

C. F.d

D. 2F.d

Answer : Option C
Explaination / Solution:

Work done = force in the direction of displacement multiplied by displacement

$W = \vec{F} . \vec{d}$

Motion in A Plane Prepare / Learn

Q10. To find the sum of vectors A and B, we place vector B

A. so that its tail is at the head of the vector A

B. so that its tail is at the tail of the vector A

C. so that its direction is the same as that of vector A

D. so that its head is at the head of the vector A

Answer : Option A
Explaination / Solution:

Triangle law of vector addition states that when two vectors are represented by two sides of a triangle in magnitude and direction taken in same order then third side of that triangle represents in magnitude and direction the resultant of the vectors.

Taken in same order mean tail of Vector B must coincide with head of vector A as shown in image.

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