Explanation

(a)(i) Photoelectric emission is the ejection of electrons from the surface of a metal when light of appropriate wavelength and frequency is incident on the metal.

(ii) Applications of photoelectric emission i.e. photo cells:

- Burglar alarms

- Photo meters

- Automatic doors

- Sound production from film tracks

- T.V. camera etc

(b)

When light of a set wavelength and frequency falls on the cathode, electrons are emitted. The electrons flow toward the anode. The flow of these electrons constitute current.

(c) (i) For energy of light with frequency less than threshold frequency, complete absorption takes place. The energy absorbed is used to raise the energy of electrons or overcome the potential barrier in the photoelectric material.

(ii) The number of emitted electrons are affected by:

- intensity

- Number of photons.

Correct Answer: A. saturated vapour pressure equals the atmospheric pressure

Correct Answer: C. increased steadily

Correct Answer: A. potential energy

Explanation

Potential energy is the energy that is stored in an object due to its position relative to some zero position.

Explanation

(a) Boiling point of a liquid is the temperature at which saturated vapour pressure of a liquid equals the external atmospheric pressure.

(b) Fill a round bottom flask partially with water, then pump out the air gradually with a vacuum pump. At a state when the saturation vapour pressure equal atmospheric pressure, the water is observed to be boiling.

(c) Application of i expansion of metals are in:

- Riveting two or more metal plates.

- Fixing of metal rims on metal wheels.

- Fusing of platinum wire through walls of glass vessels.

- Automatic fire alarms and

- Thermostat.

(d)(i) Volume = \(\frac{Mass}{Density} = \frac{250}{1.25}\)

= 200\(m^2\)

But volume = Ibh

h = \(\frac{v}{Ib} = \frac{200}{7 \times 10}\)

= 2.86m

(ii) Q = mc\(\theta\)

V = 250 x 1010(34 - 24)

= 252500 or 2.525 x 10\(^6\)

(iii) The actual energy value will be higher in value than the calculated value because --Part of heat is extracted. from the walls in the room and other materials. he room also is not airtight, there are heat leakages in and out of the room.

Explanation

t = \(\frac{Usin\theta}{g} = \frac{150 sin 30^o}{10} = 7.5s\)

Correct Answer: D. 9.0 x 10^-4N

Explanation

F \(\alpha \frac{1}{r^2}\)

therefore, \(\frac{F_1}{F_2}\) = \(\frac{r_1}{(r_2)^2}\)

\(\frac{10^{-4}}{F_2}\) = \(\frac{(0.06)^2}{(0.18)^2}\)

F = 9 x 10^-4N

Explanation

(a)(i) Laws of solid friction states that:

— friction opposes motion

— friction depends on the nature of e surfaces

— friction is independent of the area of the surfaces in contact

— frictional force F is proportional to the normal reaction R

— friction is dependent of relative velocity between the surfaces.

ii) Advantages of friction:

— it prevents man from ipping when walking

— it provides gripping effect of beIts in machines

— for grinding when using grinding ones

— used for the production of electric charges used in the brake systems of vehicles etc.

iii) Methods of reducing friction:

— by lubrication by streamlining

— by smoothing

— by using ball bearings or rollers.

b)

(c)(i) Efficiency = \(\frac{\text{Work output}}{\text{work output}}\) x 100%

= \(\frac{\text{load x distance by load}}{\text{effort x distance moved by effort}}\)

= M.A x \(\frac{1}{VR} \times \frac{100 %}{1}\)

(ii) \(e = \frac{\text{Work output}}{\text{Work input}}\) x 100

Work input = \(\frac{\text{Work output}}{E}\) x 100

= \(\frac{300 \times 10 \times 4 \times 100}{80}\)

= 15,000J or 15KJ

Correct Answer: D. the molecules of gas are all identical and are very small in size

Explanation

The wave particle paradox supposes that light exhibits wave properties such as reflection, diffraction, interference etc. and can also exist as a particle called photons. However light cannot behave as a wave and as particle at the same time.