List of top Questions asked in CBSE Class XI

State with reasons, whether the following algebraic operations with scalar and vector physical quantities are meaningful:

(a) adding any two scalars,

(b) adding a scalar to a vector of the same dimensions,

(c) multiplying any vector by any scalar,

(d) multiplying any two scalars,

(e) adding any two vectors,

(f) adding a component of a vector to the same vector

Read each statement below carefully and state with reasons, if it is true or false:
(a) The magnitude of a vector is always a scalar.
(b) each component of a vector is always a scalar
(c) the total path length is always equal to the magnitude of the displacement vector of a particle.
(d) the average speed of a particle (defined as total path length divided by the time taken to cover the path) is either greater or equal to the magnitude of average velocity of the particle over the same interval of time,
(e) Three vectors not lying in a plane can never add up to give a null vector

Pick out the two scalar quantities in the following list:
Force, angular momentum, work, current, linear momentum, electric field, average velocity, magnetic moment, relative velocity.

Pick out the only vector quantity in the following list:
Temperature, pressure, impulse, time, power, total path length, energy, gravitational potential, coefficient of friction, charge.

State, for each of the following physical quantities, if it is a scalar or a vector:
Volume, mass, speed, acceleration, density, number of moles, velocity, angular frequency, displacement, angular velocity.

A hole is drilled in a copper sheet. The diameter of the hole is 4.24 cm at 27.0 °C. What is the change in the diameter of the hole when the sheet is heated to 227 °C? Coefficient of linear expansion of copper = 1.70 × \(10^{-5} K^{-1}.\)

Three girls skating on a circular ice ground of radius 200 m start from a point P on the edge of the ground and reach a point Q diametrically opposite to P following different paths as shown in Fig. 3.19. What is the magnitude of the displacement vector for each? For which girl is this equal to the actual length of the path skated?

Figure 2.15 gives a speed-time graph of a particle in motion along a constant direction. Three equal intervals of time are shown. In which interval is the average acceleration greatest in magnitude? In which interval is the average speed greatest ? Choosing the positive direction as the constant direction of motion, give the signs of v and a in the three intervals. What are the accelerations at the points A, B, C and D ?

Suggest a suitable physical situation for each of the following graphs :

How many significant figures are present in the following?
(i) 0.0025
(ii) 208
(iii) 5005
(iv) 126,000
(v) 500.0
(vi) 2.0034

Round up the following upto three significant figures:
(i) 34.216
(ii) 10.4107
(iii) 0.04597
(iv) 2808

Express the following in the scientific notation:
(i) 0.0048
(ii) 234,000
(iii) 8008
(iv) 500.0
(v) 6.0012

What do you mean by significant figures?

What is the SI unit of mass? How is it defined?

Pressure is determined as force per unit area of the surface. The SI unit of pressure, pascal is as shown below:
\(1\text{Pa} = 1\text{N m}^{–2} \)
If mass of air at sea level is \(1034\, \text{g cm}^{–2}\), calculate the pressure in pascal.

If the density of methanol is \(0.793\, \text{kg L}^{–1}\), what is its volume needed for making 2.5 L of its 0.25 M solution?

In three moles of ethane \((\text{C}_2\text{H}_6)\), calculate the following:
(i) Number of moles of carbon atoms.
(ii) Number of moles of hydrogen atoms.
(iii) Number of molecules of ethane.

A large steel wheel is to be fitted on to a shaft of the same material. At 27 °C, the outer diameter of the shaft is 8.70 cm and the diameter of the central hole in the wheel is 8.69 cm. The shaft is cooled using ‘dry ice’. At what temperature of the shaft does the wheel slip on the shaft? Assume coefficient of linear expansion of the steel to be constant over the required temperature range : α\(_{steel}\)= 1.20 × 10\(^{-5}\) K\(^{-1}\).

Calculate the atomic mass (average) of chlorine using the following data:
% Natural Abundance Molar Mass
\(^{35}\text{Cl}\) 75.77 34.9689
\(^{37}\text{Cl}\) 24.23 36.9659

A steel tape 1m long is correctly calibrated for a temperature of 27.0 °C. The length of a steel rod measured by this tape is found to be 63.0 cm on a hot day when the temperature is 45.0 °C. What is the actual length of the steel rod on that day ? What is the length of the same steel rod on a day when the temperature is 27.0 °C ? Coefficient of linear expansion of steel = 1.20 × 10\(^{-5}\) K\(^{-1}\).

How much copper can be obtained from 100 g of copper sulphate \((\text{CuSO}_4)\)?

Two ideal gas thermometers A and B use oxygen and hydrogen respectively. The following observations are made :

Temperature	Pressure thermometer A	Pressure thermometer B
Triple-point of water	1.250 × 10\(^5\) Pa	0.200 × 10\(^5\) Pa
Normal melting point of sulphur	1.797× 10\(^5\) Pa	0.287 × 10\(^5\) Pa

What is the absolute temperature of normal melting point of sulphur as read by thermometers A and B?
What do you think is the reason behind the slight difference in answers of thermometers A and B ? (The thermometers are not faulty). What further procedure is needed in the experiment to reduce the discrepancy between the two readings?

Calculate the mass of sodium acetate \((\text{CH}_3\text{COONa})\) required to make 500 mL of 0.375 molar aqueous solution. Molar mass of sodium acetate is \(82.0245\, \text{g mol}^{–1}.\)

Calculate the mass per cent of different elements present in sodium sulphate \((\text{Na}_2\text{SO}_4)\).

Calculate the molar mass of the following:
(i) \(\text{H}_2\text{O}\) (ii) \(\text{CO}_2\) (iii) \(\text{CH}_4\)