List of top Physics Questions asked in CBSE Class XI

Two cylinders A and B of equal capacity are connected to each other via a stopcock. A contains a gas at standard temperature and pressure. B is completely evacuated. The entire system is thermally insulated. The stopcock is suddenly opened. Answer the following 1) What is the final pressure of the gas in A and B? 2) What is the change in internal energy of the gas? 3) What is the change in the temperature of the gas? 

A cylinder with a movable piston contains 3 moles of hydrogen at standard temperature and pressure. The walls of the cylinder are made of a heat insulator, and the piston is insulated by having a pile of sand on it. By what factor does the pressure of the gas increase if the gas is compressed to half its original volume?

Explain why

 (a) Two bodies at different temperatures T1 and T2 if brought in thermal contact do not necessarily settle to the mean temperature \(\frac{(T1 + T2 )}{2}\). 

(b) The coolant in a chemical or a nuclear plant (i.e., the liquid used to prevent the different parts of a plant from getting too hot) should have high specific heat. 

(c) Air pressure in a car tyre increases during driving. 

(d) The climate of a harbour town is more temperate than that of a town in a desert at the same latitude.

What amount of heat must be supplied to \(2.0 × 10^–2\) kg of nitrogen (at room temperature) to raise its temperature by 45 °C at constant pressure ? (Molecular mass of \(N_2\) = 28; R = 8.3 J \(mol^{–1} K^{–1}\).)
A geyser heats water flowing at the rate of 3.0 litres per minute from 27 °C to 77 °C. If the geyser operates on a gas burner, what is the rate of consumption of the fuel if its heat of combustion is 4.0 × 104 J/g ?
A rocket is fired vertically with a speed of 5 km s-1 from the earth’s surface. How far from the earth does the rocket go before returning to the earth ? Mass of the earth = 6.0 × 1024 kg; mean radius of the earth = 6.4 × 106 m; G = 6.67 × 10–11 N m2 kg–2
Read each statement below carefully and state with reasons and examples, if it is true or false ; 
A particle in one-dimensional motion 
  1. with zero speed at an instant may have non-zero acceleration at that instant 
  2. with zero speed may have non-zero velocity, 
  3. with constant speed must have zero acceleration, 
  4. with positive value of acceleration must be speeding up.
A player throws a ball upwards with an initial speed of 29.4 m \(\text s^{-1}\). 
  1. What is the direction of acceleration during the upward motion of the ball ?
  2. What are the velocity and acceleration of the ball at the highest point of its motion ?
  3. Choose the x = 0 m and t = 0 s to be the location and time of the ball at its highest point, vertically downward direction to be the positive direction of x-axis, and give the signs of position, velocity and acceleration of the ball during its upward, and downward motion.
  4. To what height does the ball rise and after how long does the ball return to the player’s hands ? (Take g = 9.8 \(\text m \;\)\(\text s^{-2}\) and neglect air resistance).
Fill in the blanks by suitable conversion of units  
  1. 1 \(\text {kg}\) \(\text m^{2}\text s^{-2}\) = _______ \(\text g\) \(\text{cm}^2\text s^{-2}\) .
  2. 1 \(\text m\) = ______ly.
  3. 3.0 \(\text m^{2}\text s^{-2}\) = ________ \(\text {km}\) \(\text h^{-2}\)
  4. G = 6.67 × \(10^{-11}\) N \(\text m^2\) \((\text{kg})^{-2}\) =_______ \((\text{cm})^3\text s^{-2} \text g^{-1}\).
A famous relation in physics relates ‘moving mass’ \(\text m\) to the ‘rest mass’ \(\text m_0\) of a particle in terms of its speed v and the speed of light, \(\text c\) . (This relation first arose as a consequence of special relativity due to Albert Einstein). A boy recalls the relation almost correctly but forgets where to put the constant \(\text c\). He writes : \(\text m\) = \(\frac{\text m_0}{(1-v^2)^{\frac{1}{2}}}\) . Guess where to put the missing \(\text c\).
The mass of a box measured by a grocer’s balance is 2.30 kg. Two gold pieces of masses 20.15 \(\text g\) and 20.17 \(\text g\) are added to the box. What is 
  1. the total mass of the box, 
  2. the difference in the masses of the pieces to correct significant figures ?
Fill in the blanks 
  1. The volume of a cube of side 1 cm is equal to________\(m^3\).
  2. The surface area of a solid cylinder of radius 2.0 cm and height 10.0 cm is equal to__________\(\text(mm)^2\).
  3. A vehicle moving with a speed of 18 km \(h^{-1}\) covers ________m in 1 s.
  4. The relative density of lead is 11.3. Its density is ....g \(\text {cm}^{-3}\) or ________kg \(\text m^{-3}\).
A car moving along a straight highway with speed of 126 \(\text{km}\;\text h^{-1}\) is brought to a stop within a distance of 200 \(\text m\). What is the retardation of the car (assumed uniform), and how long does it take for the car to stop ?
A drunkard walking in a narrow lane takes 5 steps forward and 3 steps backward, followed again by 5 steps forward and 3 steps backward, and so on. Each step is 1 m long and requires 1 s. Plot the x-t graph of his motion. Determine graphically and otherwise how long the drunkard takes to fall in a pit 13 m away from the start.
A woman starts from her home at 9.00 am, walks with a speed of 5 km \(\text{h}^{-1}\)on a straight road up to her office 2.5 km away, stays at the office up to 5.00 pm, and returns home by an auto with a speed of 25 \(\text {km}\) \(\text{h}^{-1}\). Choose suitable scales and plot the x-t graph of her motion.
The position-time (x-t) graphs for two children A and B returning from their school O to their homes P and Q respectively are shown in Fig. 2.9. Choose the correct entries in the brackets below ; 
  1. (A/B) lives closer to the school than (B/A) 
  2. (A/B) starts from the school earlier than (B/A) 
  3. (A/B) walks faster than (B/A) 
  4. A and B reach home at the (same/different) time 
  5. (A/B) overtakes (B/A) on the road (once/twice).
     
position-time (x-t) graph
In which of the following examples of motion, can the body be considered approximately a point object:
One mole of an ideal gas at standard temperature and pressure occupies 22.4 L (molar volume). What is the ratio of molar volume to the atomic volume of a mole of hydrogen ? (Take the size of hydrogen molecule to be about 1 \(\text\AA\) ). Why is this ratio so large ?
The unit of length convenient on the atomic scale is known as an angstrom and is denoted by \(\AA\) : 1 \(\AA\) = \(10^{-10}\;\text m\). The size of a hydrogen atom is about 0.5\(\AA .\) What is the total atomic volume in m3 of a mole of hydrogen atoms ?
The photograph of a house occupies an area of 1.75 \(\text{cm}^2\) on a 35 mm slide. The slide is projected on to a screen, and the area of the house on the screen is 1.55 \(\text m^2\). What is the linear magnification of the projector-screen arrangement.
A student measures the thickness of a human hair by looking at it through a microscope of magnification 100. He makes 20 observations and finds that the average width of the hair in the field of view of the microscope is 3.5 mm. What is the estimate on the thickness of hair ?
Which of the following is the most precise device for measuring length : 

a vernier calipers with 20 divisions on the sliding scale  
a screw gauge of pitch 1 mm and 100 divisions on the circular scale
an optical instrument that can measure length to within a wavelength of light ?

A new unit of length is chosen such that the speed of light in vacuum is unity. What is the distance between the Sun and the Earth in terms of the new unit if light takes 8 min and 20 s to cover this distance ?
Explain this statement clearly : “To call a dimensional quantity ‘large’ or ‘small’ is meaningless without specifying a standard for comparison”. In view of this, reframe the following statements wherever necessary : 
  1. atoms are very small objects 
  2. a jet plane moves with great speed 
  3. the mass of Jupiter is very large 
  4. the air inside this room contains a large number of molecules 
  5. a proton is much more massive than an electron 
  6. the speed of sound is much smaller than the speed of light.
A calorie is a unit of heat (energy in transit) and it equals about 4.2 J where 1J = 1 \(\text {kg} \;\text m^2\; \text s^{-2}.\) Suppose we employ a system of units in which the unit of mass equals \(\alpha\) kg, the unit of length equals \(\beta\) m, the unit of time is \(\gamma\) s. Show that a calorie has a magnitude 4.2 \(\alpha^{-1}\; \beta^{-2}\; \gamma^{2}\) in terms of the new units.