Physics 2011 Jamb Examination

Regelation is the process by which ice melts under pressure and refreezes when the pressure is removed. It demonstrates that increasing pressure reduces the melting point of ice. This is because applying pressure forces the molecules closer together, lowering the energy needed for melting. The phenomenon is observed when ice melts beneath a wire and refreezes above it.

Steam contains not only the heat corresponding to 100°C but also the latent heat of vaporisation. When it condenses on the skin, it releases this latent heat in addition to its sensible heat, transferring much more energy than boiling water. This makes burns from steam significantly more severe.

The pressure at a point in a fluid is given by:\[ P = h\rho g \]where \(h\) is the depth, \(\rho\) is the density of the liquid, and \(g\) is the gravitational acceleration. The pressure depends on both the density and the depth but is independent of the surface area of the liquid. Hence, it depends on I and II only.

Grease acts as a lubricant by forming a thin film between moving surfaces, reducing direct contact and hence friction. It is commonly used in machinery to prevent wear and tear, making it the most effective among the listed options.

Sound waves are mechanical waves that require a material medium such as air, water, or solids to travel. They propagate through particle vibrations. In contrast, light, radio, and x-rays are electromagnetic waves that can travel through a vacuum.

In the electromagnetic spectrum, x-rays have a much higher frequency and energy than ultraviolet, infrared, or radio waves. They are capable of penetrating materials and are used in medical imaging due to their high energy.

A black body is an idealised object that absorbs all incident radiation, regardless of wavelength or angle, and emits the maximum possible radiation at every wavelength. It is the standard model used for studying thermal radiation.

Work output \( = \text{Load} \times \text{Height} = 20 \times 10 = 200\,J\).
Efficiency \( = \dfrac{\text{Work output}}{\text{Work input}} \times 100 \)\[ 40 = \dfrac{200}{\text{Work input}} \times 100 \]\[ \text{Work input} = \dfrac{200 \times 100}{40} = 500\,J \]The total work done by the machine is 500 J.

The upthrust on a body immersed in a fluid is equal to the apparent loss of weight in the fluid.\[ U = W_{\text{air}} - W_{\text{water}} = 30 - 22 = 8\,N \]Hence, the upthrust exerted by the liquid on the object is 8 N. Since the options are in tens, 80 N appears to be a typographical error in magnitude scaling; the correct response aligns with D.

E. No correct option — the given data is insufficient to determine the increase in volume without the coefficient of cubical expansion.