NEET Previous Year Questions (2014-22): Thermal Properties of Matter | Physics Class 11 PDF Download

2024

Q1: The following graph represents the T-V curves of an ideal gas (where T is the temperature and V the volume) at three pressures P₁,P₂ and P₃ compared with those of Charles's law represented as dotted lines.            [2024]
Then the correct relation is :
(a) P₃ > P₂> P₁
(b) P₁ > P₃ > P₂
(c) P₂ > P₁ > P₃
(d) P₁ > P₂ > P₃
Ans:

2022

Q1: The energy that will be ideally radiated by a 100 kW transmitter in 1 hour is  
(a) 36 × 10⁴ J
(b) 36 × 10⁵ J
(c) 1 × 10⁵ J
(d) 36 × 10⁷ J                   [2022]
Ans: (d)
Energy = Power × time
E = 100 × 10³ × 3600  
= 36 × 10⁷ J
 

2021

Q1: A cup of coffee cools from 90°C to 80°C in t minutes, when the room temperature is 20°C. The time taken by a similar cup of coffee to cool from 80°C to 60°C at room temperature same at 20°C.     [2021]
(a) 10/13t
(b) 5/13t
(c) 13/10t
(d) 13/5t
Ans: (d)
According to Newton's law of cooling,

For 1^st cup of coffee,

For 2^nd cup of coffee,

Divide (1) by (2),

2020

Q1: The quantities of heat required to raise the temperature of two solid copper spheres of radii r₁ and r₂ (r₁ = 1.5 r₂) through 1 K are in the ratio:     [2020]
(a) 3/2
(b) 5/3
(c) 27/8
(d) 9/4
Ans: (c)
Q = msΔT s is same as material is same

2019

Q1: A copper rod of 88 cm and an aluminium rod of unknown length have their increase in length independent of increase in temperature. The length of aluminium rod is:       [2019]
(^αC_u = 1.7 × 10^-5 K^-1 and α_Al = 2.2 × 10^-5 K^-1)
(a) 6.8 cm
(b) 113.9 cm
(c) 88 cm
(d) 68 cm
Ans: (d)
Solution:
α_CuL_Cu = α_AlL_Al
1.7 × 10^–5 × 88 cm = 2.2 × 10^-5 × L_Al

2018

Q1: The power radiated by a black body is P and it radiates maximum energy at wavelength  If the temperature of the black body is now changed so that it radiates maximum energy at wavelength  , the power radiated by it becomes nP. The value of n is:-    [2018]
(a) 3/4
(b) 4/3
(c) 256/81
(d) 81/256
Ans: (c)
Solution:

2017

Q1: A spherical black body with a radius of 12 cm radiates 450 watt power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be:-    [2017]
(a) 450
(b) 1000
(c) 1800
(d) 225
Ans: (a)
Solution:


Q2: Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are K₁ and K₂. The thermal conductivity of the composite rod will be:-    [2017]

(a)
(b) K₁ + K₂
(c) 2(K₁ + K₂)
(d)
Ans: (d)
Solution:

2016

Q1: Coefficient of linear expansion of brass and steel rods are α₁ and α₂ . Lengths of brass and steel rods are ℓ₁ and ℓ₂ respectively. If (ℓ₂ - ℓ₁ ) is maintained same at all temperatures, which one of the following relations holds good ?    [2016]
(a) α₁ℓ₁ = α₂ℓ₂
(b) α₁ℓ₂ = α₂ℓ₁
(c) α₁ℓ₂² = α₂ℓ₁²
(d) α₁²ℓ₂ = α₂²ℓ₁
Ans: (a)
Solution:
Coefficient of linear expansion of brass = α₁
Coefficient of linear expansion = α₂
Length of brass and steel rods are l₁ and l₂ respectively.
Given,
Increase in length (l₂'-l₁' ) is same for all temperature.
So,


Q2: A piece of ice falls from a height h so that it melts completely. Only one-quarter of the heat produced is absorbed by the ice and all energy of ice gets converted in to heat during its fall. The value of h is : [Latent heat of ice is 3.4 x 10⁵ J/Kg and g = 10 N/kg]    [2016]
(a) 68 km
(b) 34 km
(c) 544 km
(d) 136 km
Ans: (d)
Solution:
As per conservation of energy, energy gained by the ice during its fall from height h is given by, E = mgh,
Given, only one-quarter of its energy is absorbed by the ice.
So


Q3: A block body is at a temperature of 5760 K. The energy of radiation emitted by the body at wavelength 250 nm is U₁ at wavelength 500 nm is U₂ and that at 1000 nm is U₃. Wien's constant, b = 2.88 x 10⁶ nmK. Which of the following is correct?     [2016]
(a) U₁ > U₂
(b) U₁ = 0
(c) U₃ = 0
(d) U₂ > U₁
Ans: (d)
Solution:
Given, temperature, T₁ = 5760 K
Given that energy of radiation emitted by the body at wavelength 250 nm in U₁, at wavelength 500 nm is U₂ and that at 1000 nm is U₃.
Now, according to Wein's law, we get

where, b = Wien's constant = 2.88 x 10⁶ nmK

λ_m is the wavelength corresponding to maximum energy, so U₂ > U₁.
Given, temperature, T₁ = 5760 K
Given that energy of radiation emitted by the body at wavelength 250 nm in U1, at wavelength 500 nm is U₂ and that at 1000 nm is U₃.
Now, according to Wein's law, we get
λ_mT =b
where, b = Wien's constant = 2.88 x 10⁶ nmK 

λ_m is the wavelength corresponding to maximum energy, so U₂ > U₁.

Q3: Two identical bodies are made of a material for which the heat capacity increases with temperature. One of these is at 100°C, while the other one is at 0°C. If the two bodies are brought into contact, then, assuming no heat loss, the final common temperature is    [2016]
(a) 50°C
(b) more than 50°C
(c) less than 50°C but greater than 0°C
(d) 0°C
Ans: (b)
Since, heat capacity of material increases with increase in temperature so, body at 100°C has more heat capacity than body at 0°C. Hence, final common temperature of the system will be closer to 100°C.
∴ Tc > 50°C

Q4: A body cools from a temperature 3T to 2T in 10 minutes. The room temperature is T. Assume that Newton’s law of cooling is applicable. The temperature of the body at the end of next 10 minutes will be     [2016]
(a) 7/4T
(b) 3/2T
(c) 4/3T
(d) T
Ans: (b)
According to Newton’s law of cooling,

So,

Dividing eqn. (i) by eqn. (ii), we get

2015

Q1: The two ends of a metal rod are maintained at temperatures 100^oC and 110^oC. the rate of heat flow in the rod is found to be 4.0 J/s. If the ends are maintained at temperatures 200^oC and 210^oC, the rate of heat flow will be:    [2015]
(a) 4.0 J/s
(b) 44.0 J/s
(c) 16.8 J/s
(d) 8.0 J/s
Ans: (a)
Solution:
Here, ΔT₁ = 110-100 = 10^o C

As the rate of heat flow is directly proportional to the temperature difference and the temperature difference in both the cases is same i.e. 10^o C. So, the same rate of heat will flow in the second case.
Hence,

As the rate of heat flow is directly proportional to the temperature difference and the temperature difference in both the cases is same i.e. 10^o C. So, the same rate of heat will flow in the second case.
Hence,

Q2: The value of coefficient of volume expansion of glycerin is 5 ×10^–4 K^–1. The fractional change in the density of glycerin for a rise of 40°C in its temperature, is     [2015]
(a) 0.025
(b) 0.010
(c) 0.015
(d) 0.020
Ans:  (d)
Let ρ₀ and ρ_T be densities of glycerin at 0°C and T °C respectively. Then,

where γ is the coefficient of volume expansion of glycerine and ΔT is rise in temperature.

Q3: On observing light from three different stars P, Q and R, it was found that intensity of violet colour is maximum in the spectrum of P, the intensity of green colour is maximum in the spectrum of R and the intensity of red colour is maximum in the spectrum of Q. If T_P, T_Q and T_R are the respective absolute temperatures of P, Q and R, then it can be concluded from the above observations that:    [2015]
(a) T_P < T_Q < T_R
(b) T_P > T_Q > T_R
(c) T_P > T_R > T_Q
(d) T_P < T_R < T_Q
Ans: (b)
Solution:

2014

Q1: Light with an energy flux of 25 x 10⁴Wm⁻² falls on a perfectly reflecting surface at normal incidence. If the surface area is 15 cm², the average force exerted on the surface is    [2014]
(a) 1.20 x 10⁻⁶ N
(b) 3.0 x 10⁻⁶ N
(c) 1.25 x 10⁻⁶ N
(d) 2.50 x 10⁻⁶ N
Ans: (d)
Solution:

Q2: Certain quantity of water cools from 70°C to 60°C in the first 5 minutes and to 54° C in the next 5 minutes. The temperature of the surroundings is    [2014]
(a) 42°C
(b) 10°C
(c) 45°C
(d) 20°C
Ans: (c)
Solution: