JAMB Physics 2006 Past Questions & Answers

To determine if the cube will float or sink, we must compare its density to the density of water. The volume of the cube is 10cm x 10cm x 10cm = 1000 cm³. Its density is mass divided by volume, which is 700g / 1000 cm³ = 0.7 g/cm³. Since the cube's density (0.7 g/cm³) is less than the density of water (which is 1.0 g/cm³), the cube will float.

Common mistake: Students may mistakenly choose option C by assuming any solid object sinks, without first calculating the cube's density to compare it with the density of water.

Humidity is the measure of water vapour in the air. When humidity is low, the air is dry and can easily absorb more moisture. This causes sweat and water to evaporate very quickly from the surface of the skin, leaving the skin feeling dry and often rough.

Common mistake: Students might confuse the effects of low humidity with high humidity, where high moisture content in the air prevents sweat from evaporating, leaving the skin feeling damp.

First, find the density of gold using the formula: Density = Relative Density × Density of water. Since the density of water is 1000 kg/m³, the density of gold is 19.2 × 1000 = 19200 kg/m³. Next, use the formula Volume = Mass / Density to find the volume. So, the volume of gold is 2.4 kg divided by 19200 kg/m³, which gives 0.000125 m³ or 1.25 × 10⁻⁴ m³.

Common mistake: A common mistake is to incorrectly divide the relative density by the mass $(19.2 ÷ 2.4 = 8)$ and then mistakenly select the option that starts with 8, ignoring the correct formula.

A thermometric property is a physical property that changes consistently and measurably with temperature. In a constant volume thermometer, the volume of the gas is kept fixed. According to the Pressure Law (or Gay-Lussac's Law), the pressure of a fixed mass of gas at constant volume is directly proportional to its absolute temperature. Therefore, the change in pressure is the property used to determine the temperature.

Common mistake: Students often mistakenly choose 'change in volume' because they confuse the constant volume thermometer with the constant pressure thermometer, where volume is the thermometric property.

To find the time taken, we equate the electrical energy supplied by the heater to the heat energy absorbed by the water. The electrical energy is Power × time (E = P × t = IVt), and the heat energy absorbed is Q = mcΔθ. So, IVt = mcΔθ. Plugging in the values: (2.0 A × 240 V) × t = 2.5 kg × $(4.2 × 10³ J kg⁻¹ K⁻¹)$ × $(100 - 52)°C$. This simplifies to 480 × t = 504,000 J, so t = 504,000 / 480 = 1050 s, which is 1.05 × 10³ s.

Common mistake: Students often make a calculation error or mistake the power of ten when converting the final answer to standard form, leading them to incorrectly choose an option like 1.05 × 10² s.

A thermos flask is specially built to keep its contents at a steady temperature by stopping heat from moving between the contents and the outside environment. It does this by tackling all three ways heat can travel: the vacuum between its double walls stops heat transfer by conduction and convection, and the shiny, silvered surfaces reduce heat transfer by radiation. This design prevents heat from getting out (loss) and from getting in (gain).

Common mistake: Students often mistakenly choose options C or D because they only think about one function of the flask, like keeping tea hot (preventing heat loss), and forget that it also keeps cold drinks cold (preventing heat gain).

A thermometer works because the liquid inside usually expands more than the glass when heated, causing the liquid to rise. In this unusual case, the glass container expands more than the liquid. This means the space inside the thermometer gets bigger faster than the liquid can fill it, so the level of the liquid will fall or go down in the stem.

Common mistake: Students often mistakenly choose C because they remember that heating a normal thermometer makes the liquid rise, but they fail to consider the question's special condition where the glass expands more than the liquid.

For a liquid to change into a gas, a process called evaporation, it must absorb heat from its surroundings. This required heat is known as the latent heat of vaporization. Petrol evaporates much more quickly than water, so it rapidly draws this heat energy from your finger, making it feel cold.

Common mistake: Students might mistakenly choose option B because they confuse the latent heat of vaporization (for liquid turning to gas) with the latent heat of fusion (for solid turning to liquid).

According to the maximum power transfer theorem, a source like a cell with an internal resistance 'r' will deliver the most power to an external resistor 'R' when the external resistance is equal to the internal resistance. This condition provides the best balance between the current flowing in the circuit and the voltage across the external resistor. Therefore, for maximum power to be transferred from the cell to the resistor, R must be equal to r.

Common mistake: Students often mistakenly believe that a larger external resistor (R > r) is needed to get more power, confusing power with voltage, but this actually reduces the overall current and thus the power delivered to the resistor.

An atom is naturally neutral because it has an equal number of positive protons and negative electrons. Objects become charged only when electrons are transferred, as they are the mobile particles. A body that gains extra electrons has a surplus and becomes negatively charged, while a body that loses electrons has a deficiency and becomes positively charged.

Common mistake: Students may mistakenly choose option C, thinking that positive charge is due to adding protons, but they forget that protons are tightly bound in the atom's nucleus and cannot be easily transferred like electrons.