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Practice each question, then open the answer or worked solution.
Refer to the plot of temperature versus time showing the changes in the state of ice on heating. Which of the following is correct?
The correct answers are
a) the region AB represents ice and water in thermal equilibrium
d) C to D represents water and steam in equilibrium at boiling point
A glass full of hot milk is poured on the table. It begins to cool gradually. Which of the following is correct?
The correct answers are
b) the temperature of milk falls off exponentially with time
c) while cooling, there is a flow of heat from milk to the surrounding as well as from surrounding to the milk but the net flow of heat is from milk to the surrounding and that is why it cools
d) all three phenomena, conduction, convection, and radiation are responsible for the loss of heat from milk to the surroundings
Very Short AnswersIs the bulb of a thermometer made of diathermic or adiabatic wall?
The bulb of a thermometer is made of diathermic walls as they allow the conduction of the heat.
A student records the initial length l, change in temperature ∆T and change in length ∆l of a rod as follows:
| Sl.no | l (m) | ∆T (oC) | ∆l (m) |
| 1 | 2 | 10 | 4 × 10-4 |
| 2 | 1 | 10 | 4 × 10-4 |
| 3 | 2 | 20 | 2 × 10-4 |
| 4 | 3 | 10 | 6 × 10-4 |
If the first observation is correct, what can you say about observations 2, 3, and 4.
It is given that the first observation is correct which means that the coefficient of linear expansion is
For second observation,
Which is incorrect
For third observation,
Which is incorrect
For fourth observation,
Which is correct
Why does a metal bar appear hotter than a wooden bar at the same temperature? Equivalently it also appears cooler than wooden bar if they are both colder than room temperature.
A metal bar appears to be hotter than a wooden bar at the same temperature because the rate of transfer of heat in a metal is faster than in the wood. Similarly, metal bar appears to be colder than the wooden bar as the specific heat of the metal is very low than the wood.
Calculate the temperature which has same numerical value on Celsius and Fahrenheit scale.
Consider two fixed points for the construction of the scale of temperature.
The first fixed point is for the freezing point which is known as lower fixed point.
The second fixed point is for the boiling point which is known as upper fixed point.
Following is the identity that is used for the conversion:
Let T be the value of temperature that has a same value for Celsius and Fahrenheit scale:
F = C = T
Using the above relation, we can calculate T = -40oF
These days people use steel utensils with copper bottom. This is supposed to be good for uniform heating of food. Explain this effect using the fact that copper is the better conductor.
Copper bottom utensils are used because copper is a good conductor of heat when it is compared with the steel. Therefore, copper bottom utensils are used and also the heat gets transferred uniformly.
Short AnswersFind out the increase in moment of inertia I of a uniform rod about its perpendicular bisector when its temperature is slightly increased by ∆T.
Above is the figure of a rod that has a uniform mass M and length l which is bisected perpendicularly.
Increase in length of the rod when the temperature is increased is given as:
New moment of inertia is given as:
Change in length is given as:
Therefore, increase in moment of inertia is given as:
During summers in India, one of the common practice to keep cool is to make ice balls of crushed ice, dip it in flavoured sugar syrup and sip it. For this a stick is inserted into crushed ice and is squeezed in the palm to make it into the ball. Equivalently in winter, in those areas where it snows, people make snow balls and throw around. Explain the formation of ball out of crushed ice or snow in the light P-T diagram of water.
The above graph is between the pressure and the temperature for water. As the pressure increases, the ice changes into liquid state and when the pressure is decreased, it changes into liquid state.
100 g of water is supercooled to -10oC. At this point, due to some disturbance mechanised or otherwise some of it suddenly freezes to ice. What will be the temperature of the resultant mixture and how much mass would freeze?
Mass of water = 100 g
At -10oC the mixture has water and ice
Heat required by the mixture is ms∆t = (100)(1)(0-(-10) = 1000 Cal
Therefore, the mass of the mixture, m = Q/L = 12.5 g