21.

Why are burns caused by the steam more severe than those caused by boiling water at the same temperature? 

i) What is meant by specific heat capacity of a substance?

ii) Why does the heat supplied to a substance during its change of state not cause any rise in its temperature. 

What will an alpha particle change into when it absorbs:

i) One electron;

ii) Two electrons?

Mention two important properties of a metal that make it good thermionic emitter. 

Name the three main parts of a hot cathode ray tube. Mention one important function of each of the three main parts. 

A block and tackle pulley system has a velocity ratio 3.

i) Draw a labelled diagram of this system. In your diagram, indicate clearly the points of application and the direction of the load and effort.

ii) Why should the lower block of this pulley system be of negligible weight.

i) With the help of a well-labelled diagram, show that the apparent depth of an object, such as a coin, in water is less than its real depth.

ii) How is the refractive index of water related to the real depth and the apparent depth of a column of water?

A cell of e.m.f. 1.5 V and internal resistance 1.0 ohm is connected to two resistors of 4 ohm and 2 ohm in series as shown in the figure.

Calculate the:

i) current in the circuit

ii) potential difference across the 4 ohm resistor.

iii) voltage drop when the current is flowing.

A substance is in the form of a solid at 0^o C. The amount of heat added to this substance and the temperature of the substance are plotted on the following graph:

If the specific heat capacity of the solid substance os 500 J/kg^o C, find from the graph:

i) the mass of the substance

i) What happens to the atomic number of an element when it emits:

1. an alpha particle;

2. a beta particle.