2025 - JAMB Physics Past Questions and Answers - page 4

According to Faraday’s first law of electrolysis, the mass deposited is directly proportional to the charge passed, so \( m = ZQ \).
Since the same current flows for the same duration in both voltameters, the charge passed is equal for both metals.
This means \( \frac{m_{\mathrm{Cu}}}{Z_{\mathrm{Cu}}} = \frac{m_{\mathrm{Ag}}}{Z_{\mathrm{Ag}}} \).
Rearranging to make \( Z_{\mathrm{Ag}} \) the subject gives \( Z_{\mathrm{Ag}} = \frac{m_{\mathrm{Ag}} \times Z_{\mathrm{Cu}}}{m_{\mathrm{Cu}}} \).
Substituting the values gives \( Z_{\mathrm{Ag}} = \frac{1.2 \times 0.00028}{0.2} \).
Multiplying gives 0.000336, and dividing by 0.2 gives 0.00168.
Therefore, the electrochemical equivalent of silver is \( 1.68 \times 10^{-3} \, \text{gC}^{-1} \).

Food contains energy stored within the bonds of its molecules.
When food is digested, chemical reactions occur that release this stored energy.
This released energy is then used by the body for movement, growth, and maintaining body functions.
Because the energy originates from chemical bonds, it is known as chemical energy.
Therefore, the energy present in food is chemical energy.

Thermal capacity is defined as the amount of heat needed to raise the temperature of a body by one degree.
It is expressed mathematically as \( C = mc \), where \( m \) is the mass and \( c \) is the specific heat capacity.
The mass determines how much substance is present, while the specific heat capacity depends on the material itself.
This shows that thermal capacity depends on both the quantity of material and the nature of the substance.
Therefore, thermal capacity depends on the nature and mass.

Temperature gradient represents the change in temperature per unit length.
The temperature difference between the ends is obtained by multiplying the gradient by the length of the rod.
This gives \( \Delta T = 416 \times 0.2 \).
Multiplying gives 83.2K.
The temperature at the other end is found by adding this temperature increase to the initial temperature.
This gives \( 233 + 83.2 = 316.2^\circ \text{C} \).
Therefore, the temperature at the other end is approximately 316.28°C.

Efficiency is defined as the ratio of useful output work to the input work supplied.
This is expressed as \( \text{Efficiency} = \frac{\text{Output Work}}{\text{Input Work}} \).
The efficiency is given as 80%, which is equal to 0.8 in decimal form.
Rearranging the formula gives \( \text{Output Work} = \text{Efficiency} \times \text{Input Work} \).
Substituting the values gives \( 0.8 \times 200 \).
This gives 160J.
Therefore, the output work is 160J.

Radiation detectors are instruments designed to identify or measure ionizing radiation.
Examples include Geiger-Muller counters, scintillation chambers, and film badges, all of which detect radiation through different physical processes.
An electrophorus, however, is used to generate static electric charge through electrostatic induction.
It does not measure or detect radiation in any form.
Therefore, the electrophorus is not a radiation detector.

Thermal conductivity describes how well a material allows heat to pass through it.
Materials with low thermal conductivity transfer heat very slowly and are considered good insulators.
Air has widely spaced molecules compared to solids and liquids, which makes heat transfer less efficient.
As a result, air conducts heat much less effectively than ash, glass, or water.
Therefore, air has the least thermal conductivity.

Standing waves occur when a wave travels and then reflects back from a surface.
The reflected wave combines with the incoming wave, and both waves have the same frequency and amplitude.
This interaction produces fixed points where no motion occurs and points where vibration is maximum.
This pattern forms what is known as a standing wave.
Therefore, standing waves are produced by waves that reflect and interfere with themselves.

A wave consists of repeating patterns of crests and troughs.
The wavelength is defined as the distance between two successive points that are in the same phase of motion.
Examples include crest to crest or trough to trough.
This distance represents one complete cycle of the wave.
Therefore, the distance between two successive troughs is one wavelength.

The heat gained by a substance is related to its mass, specific heat capacity, and temperature change by the relation \( Q = mc\Delta T \).
To find the specific heat capacity, the formula is rearranged to give \( c = \frac{Q}{m\Delta T} \).
The heat supplied is 1000J, the mass is 0.025kg, and the temperature increase is 15K.
Substituting these values gives \( c = \frac{1000}{0.025 \times 15} \).
Multiplying the denominator gives \( 0.025 \times 15 = 0.375 \).
Dividing gives \( c = \frac{1000}{0.375} = 2666.7 \).
Therefore, the specific heat capacity of the metal is 2666.7JKg\(^{-1}\)K\(^{-1}\).