Physics 2024 Jamb Examination

A hot wire ammeter is specifically designed to measure both AC and DC by utilizing the heating effect of electric current. When current flows through the fine wire in the instrument, the wire heats up and expands. This expansion causes a sag in the wire, which is linked to a pointer that moves across a scale. While an electric heater also uses the heating effect, it is an appliance, not a measuring instrument. Moving iron and galvanometers primarily rely on the magnetic effects of current rather than thermal expansion.

The perceived colour of an opaque object is determined by the wavelengths of light it reflects. A red rose appears red under white light because it absorbs all colours of the visible spectrum except red, which it reflects. Blue light contains no red wavelengths. Therefore, when blue light shines on a red rose, the rose absorbs the blue light and has no red light to reflect. Since no light is reflected back to the eye, the rose appears black.

Electric field intensity (\(E\)) is defined as the force (\(F\)) acting per unit charge (\(q\)) at a given point in the field.
br>The formula is: \[ E = \frac{F}{q} \] Given: \(F = 8 \, \text{N}\) \(q = 4\mu\text{C} = 4 \times 10^{-6} \, \text{C}\) \[ E = \frac{8}{4 \times 10^{-6}} \] \[ E = 2 \times 10^6 \, \text{NC}^{-1} \] The intensity represents the strength of the electric field at the location of the charge.

Efficiency (\(\eta\)) is the ratio of output energy to input energy. [Image representing energy flow and losses in a battery system]
The formula is: \[ \eta = \frac{\text{Energy Output}}{\text{Energy Input}} \times 100\% \] Given: \(\eta = 90\% = 0.9\) \(\text{Energy Output} = 2700 \, \text{J}\) \[ 0.9 = \frac{2700}{\text{Energy Input}} \] \[ \text{Energy Input} = \frac{2700}{0.9} = 3000 \, \text{J} \] This indicates that 300J of energy is dissipated (usually as heat) during the process, while 2700J is successfully delivered.

For capacitors connected in series, the equivalent capacitance (\(C_t\)) is calculated using the reciprocal formula. \[ \frac{1}{C_t} = \frac{1}{C_1} + \frac{1}{C_2} \] \[ \frac{1}{C_t} = \frac{1}{0.0003} + \frac{1}{0.0006} \] To simplify, find a common denominator: \[ \frac{1}{C_t} = \frac{2}{0.0006} + \frac{1}{0.0006} = \frac{3}{0.0006} \] \[ C_t = \frac{0.0006}{3} = 0.0002 \, \mu\text{F} \] When capacitors are in series, the total capacitance is always smaller than the smallest individual capacitor in the group.

Acceleration is defined as the rate of change of velocity over time. On a velocity-time (v-t) graph, the acceleration is represented by the slope of the line.
The formula for mean acceleration (\(a\)) is: \[ a = \frac{\Delta v}{\Delta t} = \frac{v_2 - v_1}{t_2 - t_1} \] Using the coordinates provided: \(t_1 = 2\,s, v_1 = 5\,m/s\) \(t_2 = 4\,s, v_2 = 15\,m/s\) \[ a = \frac{15 - 5}{4 - 2} \] \[ a = \frac{10}{2} = 5.0 \, \text{ms}^{-2} \] This value represents the constant rate at which the object's velocity increased during that two-second interval.

To find the distance travelled by the jet, we use the basic formula for linear motion at a constant speed: \[ \text{Distance} = \text{Speed} \times \text{Time} \] Given: \(\text{Speed} (v) = 335 \; \text{m/s}\) \(\text{Time} (t) = 5 \; \text{s}\) \[ \text{Distance} = 335 \times 5 = 1675 \; \text{m} \] The aircraft is 1675 metres away from the gun at the moment it is fired.

While the specific diagram isn't displayed here, in physics, a galvanometer is converted into an ammeter by connecting a low-resistance resistor (called a shunt) in parallel with it. Conversely, it is converted into a voltmeter by connecting a high-resistance resistor (called a multiplier) in series with it. Based on standard 2024 JAMB examination diagrams for this specific question, the resistor is usually shown in parallel, making it an ammeter.

In a camera, the diaphragm (or aperture) regulates the amount of light entering the lens by adjusting the size of the opening. In the human eye, the iris performs the exact same function. It is the coloured part of the eye that contracts or expands to change the size of the pupil, thereby controlling the light intensity reaching the retina. The lens of the eye corresponds to the camera lens, and the retina corresponds to the film or sensor.

The angle of dip (or magnetic inclination) is the angle that the Earth's magnetic field lines make with the horizontal plane. This angle is measured using a specialized instrument known as a dip circle. It consists of a magnetic needle pivoted at its centre of gravity so that it can rotate freely in a vertical plane. When placed in the magnetic meridian, the needle points in the direction of the Earth's total magnetic field, allowing the angle to be read on a vertical scale.