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Why should crushed ice be used in the experiment?

To increase the surface area of ice and

keep good contact with the heater.Crushed ice should be used because this enhances the

thermal contact between the ice and the heater. Therefore,

less heat is wasted to heat up the air between the ice

cubes.

Would you expect the value of the specific latent heat of fusion

of ice obtained in the experiment to be higher than, equal to,

or lower than the accepted value? Explain briefly.

The value obtained is higher than the accepted value. This is

because some energy supplied by the heater is lost to the

surroundings. The actual energy absorbed by the ice should

be lesser.

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Describe, with the aid of a diagram, how a control set can be

set up to improve the accuracy of the experiment.

An immersion heater is set up without connecting to the

power supply. The actual mass of ice melted by the energy

supplied by the heater is the mass difference between the

masses of water in the two beakers.

Why should the melting ice be used?

Melting ice is used to make sure that the temperature of theice is at 0 C. Hence, no energy is absorbed as the heat

capacity to raise the temperature of the ice to 0 C.

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Why is the control necessary?

This is to account for the ice melted at room temperature.

After switching off the heater, the cups are not removed until

the drip rates become steady. Why?

This is to allow time for the energy from the heater to be

conducted to the ice to melt it (water and ice are poor

conductors of heat).

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The immersion heater should not be switched on unless it is

fully immersed in water. Why?

Otherwise the heater may overheat and gets damaged.

What are the possible sources of error in the experiment?

Sources of Error

Calculated result

higher / lower thanaccepted value?

Steam condensing on the top of the heater

drips back into the beaker.

Higher

Some water spills out from the beaker. LowerEnergy is lost to the surroundings. Higher

Energy from the non-immersed part of the

heater is lost to the surrounding and not

transferred to the water.

Higher

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A student suggests adding a lid on the beaker so as to

improve the accuracy of the experiment.

If the beaker is covered with a lid, the steam will not be able

to escape from the beaker. As a result, water vapour will

condense on the lid and return back to the beaker. This will

lead to a serious experimental error.

Is the value of specific latent heat of vaporization obtained in

the experiment usually higher or lower than the accepted

value? Explain briefly.

Due to the heat loss to the surroundings, the energy recorded

by the kilowatt-hour meter is higher than the energy absorbed

by the water. The value obtained is usually higher than the

accepted value.

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Comment on the statement:

The calculated value of the specific latent heat of vaporization

of water should be lower than the accepted value because

some boiling spills out from the cup.

Although water may spill out from the beaker, the main source

of error is due to the heat lost to the surroundings.As the

energy supplied is always greater than the energy absorbed,

the calculated value would be greater than the accepted value.

Suggest a method to improve the accuracy of the experiment.

Use a polystyrene cup instead of a beaker because

polystyrene is a poor conductor of heat.

Wrapping the beaker with cotton wool.