2024 - JAMB Physics Past Questions and Answers - page 3

The inductive reactance (_XL) of a coil in an AC circuit is given by the formula:

X_L = 2πfL

Where:

• f is the frequency of the AC current (in Hertz)
• L is the inductance of the coil (in Henries)

Given:

• L = 7 H
• f = 50 Hz

Calculate X_L:

X_L = 2 x π x 50 x 7 ≈ 2200 Ω

The correct answer is attraction. Here's why:

• Ebonite rods and glass rods acquire different types of charges when rubbed with appropriate materials. Ebonite rods become negatively charged, while glass rods become positively charged.
• Opposite charges attract each other. Therefore, a negatively charged ebonite rod will be attracted to a positively charged glass rod.
• Repulsion occurs only between objects with the same type of charge.
• A spark may occur if the charges are strong enough and the distance is small, but it is not the primary interaction.
• There will always be a force (attraction or repulsion) between charged objects.

A liquid-in-glass thermometer uses the change in volume of a liquid (usually mercury or alcohol) with temperature to measure temperature. As the temperature increases, the liquid expands and rises up the calibrated glass tube.

Here's how to solve the problem step-by-step:

1. Calculate the total power consumption of the appliances: Total power = 80 W + 100 W + 120 W = 300 W
2. Convert to kilowatts (kW): 300 W / 1000 = 0.3 kW
3. Calculate the daily energy consumption: Daily energy = 0.3 kW x 6 hours = 1.8 kWh
4. Calculate the monthly energy consumption: Monthly energy = 1.8 kWh x 31 days = 55.8 kWh
5. Calculate the monthly bill: Bill = 55.8 x ₦24.08 ≈ ₦1343.66

The weight of an object is directly proportional to the acceleration due to gravity. Since the moon's gravity is 1/6 of Earth's, the weight of the bowling ball on the moon will also be 1/6 of its weight on Earth.

Here's how to solve the problem:

1. Identify the forces: Weight W = mg, where m = 60 kg and g ≈ 10 m/s².
2. Determine net acceleration: Lift descends at 3 m/s², so apparent acceleration = g - a = 10 - 3 = 7 m/s².
3. Calculate apparent weight: W' = m x (g - a) = 60 x 7 = 420 N.

Step-by-step solution:

1. Convert energy to SI units: Q = 288 kJ = 288,000 J
2. Cube thickness x = 3 m, time t = 7200 s, temperature gradient dT/dx = 90 °C/m
3. Area of cube face: A = 3 x 3 = 9 m²
4. Use heat conduction formula: Q = (k x A x dT/dx x t) / x
5. Rearrange for k: k = (Q x x) / (A x dT/dx x t)
6. Plug in values: k = (288000 x 3) / (9 x 90 x 7200) = 864000 / 5832000 ≈ 0.05 or 5.0 x 10^-2 W/m·K

Potential difference (emf) is directly proportional to the balancing length in a potentiometer. Set up proportion: E₁ / E₂ = L₁ / L₂

• E₁ = 3.06 V
• E₂ = 2.295 V
• L₁ = 75 cm
• L₂ = unknown

Calculate L₂: L₂ = (E₂ x L₁) / E₁ = (2.295 x 75) / 3.06 = 172.125 / 3.06 ≈ 56.25 cm

The mechanical advantage (MA) of a machine is calculated as:

MA = Output Force / Input Force

If considering work done: MA = (Load x Load Distance) / (Effort x Effort Distance)

Given: Load = 15 N, Load distance = 20 cm, Effort = 5 N, Effort distance = 10 cm

MA = (15 x 20) / (5 x 10) = 300 / 50 = 6

Note: If the intended answer from options is 30.0, it may consider alternative scaling; ensure consistency with question context.

Newton's Law of Cooling states that the rate of heat loss of a body is directly proportional to the difference in temperatures between the body and its surroundings. It is most accurate when temperature differences are small; for large differences, the law becomes less accurate.