Physics 2015 Jamb Examination

To convert a temperature from the Celsius scale to the Kelvin (absolute) scale, we use the standard conversion formula:\[ T(K) = \theta(^{\circ}\text{C}) + 273 \]Given:\[ \theta = 45^{\circ}\text{C} \]\[ T = 45 + 273 = 318\text{K} \]The temperature 45°C is equivalent to 318K on the thermodynamic temperature scale.

Weightlessness is not the absence of gravity, but rather the absence of a ground reaction force. When an astronaut or a spaceship is in orbit, they are in a state of continuous 'free fall' towards the Earth. Because both the crew and the spaceship are accelerating towards the Earth at the same rate due to gravity, there is no contact force between the crew and the floor of the ship. This condition is known as microgravity or free fall, which results in the sensation of being weightless.

Radio waves are a type of electromagnetic radiation. All electromagnetic waves, regardless of their frequency or wavelength (including light, X-rays, and radio waves), travel at the same constant speed in a vacuum. This speed is known as the speed of light, which is approximately \(3.0 \times 10^8 \text{ ms}^{-1}\). Option A is closer to the speed of sound, which is a mechanical wave and much slower.

In a longitudinal wave, such as a sound wave, the particles of the medium vibrate back and forth in the same direction that the wave travels.

This movement creates regions where the particles are crowded together, called 'compressions', and regions where the particles are spread further apart, called 'rarefactions'. These correspond to the crests and troughs of a transverse wave respectively.

Work is defined as Force multiplied by Distance. To find the dimensions, we break it down into fundamental units:\[ \text{Force} = \text{Mass} \times \text{Acceleration} \]\[= M \times LT^{-2} = MLT^{-2} \]\[ \text{Work} = \text{Force} \times \text{Distance}\]\[ = (MLT^{-2}) \times L = ML^2T^{-2} \]Comparing \(ML^2T^{-2}\) with the general form \(M^a L^b T^c\):
\(a = 1\) (exponent of Mass)
\(b = 2\) (exponent of Length)
\(c = -2\) (exponent of Time)
Therefore, the values are 1, 2, -2.

A magnetic relay is an electromagnetic switch. It uses a small current flowing through a coil to create a magnetic field, which then moves an armature to close or open the contacts of a separate, second circuit.

This allows a low-power circuit (like a computer or a small switch) to safely control a high-power or high-voltage circuit without a direct electrical connection between the two, protecting the user and the control equipment.

There are three primary modes of heat transfer. Conduction requires a solid medium (particle to particle contact). Convection requires a fluid medium (liquid or gas movement). Radiation, however, is the transfer of heat energy via electromagnetic waves (infrared). Since electromagnetic waves do not require a material medium to propagate, radiation is the only method by which heat can travel through a vacuum, such as the heat from the Sun reaching the Earth through empty space.

A calorimeter is an insulated container used in the laboratory to measure the amount of heat involved in a chemical reaction or other process. While a thermometer measures temperature (the degree of hotness), a calorimeter is used to determine the total heat energy (Q) by observing temperature changes in a known mass of water or other substance surrounding the process. Measuring cylinders are for volume, and meter rules are for length.

Lodestone is a naturally occurring magnetic oxide of iron (magnetite). Like any other magnet, when it is suspended freely so that it can rotate, it will align itself with the Earth's magnetic field. Its North-seeking pole will point towards the Earth's geographic North, and its South-seeking pole will point towards the geographic South. This North-South (N-S) alignment property is what made lodestones useful as the first primitive compasses for navigation.

In hazy or foggy conditions, visible light is easily scattered by small water droplets or dust particles in the air, resulting in blurry or obscured images. Infrared radiation has longer wavelengths than visible light, which allows it to pass through haze with significantly less scattering.
Specialized infrared-sensitive cameras can capture these rays to produce clear photographs of objects that are otherwise invisible to the naked eye or standard cameras in such conditions.