Explain the following:
(a) The surrounding become pleasantly warm when water in a lake starts freezing in cold countries.
(b) The heat supplied to a substance during its change of state, does not cause any rise in its temperature.

How does the (a) average kinetic energy (b) average potential energy of molecules of a substance change during its change in phase at a constant temperature, on heating ?

Fill in the blank spaces by choosing the correct words from the list given below: latent heat of fusion, melting point, steam, constant, latent heat of vaporisation. During the change of state of a substance its temperature remains___________.

Fill in the blank spaces by choosing the correct words from the list given below: latent heat of fusion, melting point, steam, constant, latent heat of vaporisation. The amount of heat required to change 1 g of a substance at its melting point into liquid state without any rise in temperature is called specific_________.

A cylindrical rod of heat capacity 120 J//K in a room temperature 27^(@)C is heated internally by heater of power 250W , The steady state temperature attained by the rod is 37^(@)C . Fin the following: (a) The initial rate of increse in temperature (b) The steady state rate of emission of radiant heat. If the heater is switched off, find (c) The initial rate of decrease is temperature (d) The rate of decrease in temperature of the cylinder when its temperature falls to 31^(@)C and (e) The maximum amount of heat lost by the cylinder

(a) What do you understand by the change of phase of a substance ? (b) Is there any change in temperature during the change of phase ? (c) Does the substance absorb or liberate any heat energy during the change of phase ? (d) What is the name given to the energy absorbed during a phase change ?

A substance is in the solid form at 0^@ C. The amount of heat added to this substance and its temperature are plotted in the following graph. If the relative specific heat capacity of the solid substance is 0.5, find from the graph (i) the mass of the substance, (ii) the specific latent heat of the melting process and (ii) the specific heat of the substance in the liquid state. Specific heat capacity of water =1000 cal//kg//K

Write true or false for the following statements: The process of changing a solid at its melting point into liquid state, without any rise in temperature is called fusion. ________.

An ice ball of radius a and mass m is placed at 0^@C inside a thick hollow sphere of inner and outer radii a and b whose thermal conductivity varies as k=alpha/r^2 , where alpha is a positive constant and r is the distance from centre. The temperature of surrounding is theta_0 and latent heat of fusion for ice is L_f . Then , time required to completely melt the ice ball is (Neglect the contraction in volume when ice melts into water and any change in thermal resistance due to melting of ice of the system.)

A dc motor works on the principle that a current carrying coil, when placed in a magnetic field experiences a torque. The arrangement consists of a coil suspended in a region of magnetic field. When a current is passed through the coil, it experiences torque and starts rotating. A simple arrangement is shown below. The coil rotates under the action of torque. The current is supplied to the coil by an arrangement of two sliding contacts and a split ring. As the coil rotates, the magnetic flux linked with the coil changes. This leads to production of an induced emf epsilon in the coil. By Lenz's law, the induced emf opposes the applied voltage and therefore, it is called back emf. If R is the resistance in the coil, the current i flowing through the coil at any instant is i=(V-epsilon)/(R) . The back emf is developed due to induction and it is directly proportional to speed of rotation and it is directly proportional to speed of rotation of the motor. There is a continuous power loss i^(2)R in the motor, in form of heat. When a dc motor is running unloaded (full speed) the current through it is 1 A. What will be the current flowing through the motor, when it is loaded to run at half its maximum speed, it applied voltage is 10 V and armature resistance is 5 Omega

Look at the change of state diagram from gas to solid given here carefully, and answer the following questions. a. During freezing, certain amount of heat is given out without any change in temperature. Which part of the graph shows this change? b. During condensation, certain amount of heat is given out without any change in temperature. Which part of the graph shows this change? c. Which point on the graph corresponds to İ. condensation point? ii. freezing point? d. What do ab and cd on the graph represent?