2024 - JAMB Physics Past Questions and Answers - page 3

The inductive reactance (X_L) of a coil in an AC circuit is given by the formula:X_L = 2πfLwhere:* 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 HzCalculate X_L:X_L = 2 * π * 50 Hz * 7 HX_L ≈ 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 (e.g., wool and silk, respectively). 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 only occurs between objects with the same type of charge.
• A spark may occur if the charges are strong enough and the distance is small enough, 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 = 80W + 100W + 120W = 300W

2. Convert the total power to kilowatts (kW):

   • 300W / 1000 = 0.3 kW

3. Calculate the daily energy consumption:

   • Daily energy = Power (kW) * Time (hours)
   • Daily energy = 0.3 kW * 6 hours = 1.8 kWh

4. Calculate the monthly energy consumption:

   • Monthly energy = Daily energy * Number of days in a

The weight of an object is directly proportional to the acceleration due to gravity. Since the moon's acceleration due to gravity is 1/6 of the 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: The man's weight (W) acts downwards, and the lift exerts a normal force (N) upwards. The weight is calculated as W = mg, where m is the mass and g is the acceleration due to gravity (approximately 10 m/s²).
2. Determine the net acceleration: Since the lift is descending at 3 m/s², the net acceleration acting on the man is downwards. However, this acceleration is relative to the gravitational acceleration. Therefore, the apparent acceleration will be g - a, where a is the lift's acceleration.
3. Calculate the apparent weight: The apparent weight (W') is the force the man exerts on the lift. This is calculated using Newton'

Here's how to solve the problem:1. Convert the given values into SI units: * Energy transferred, Q = 288 kJ = 288,000 J * Length, x = 3 m (This is the thickness of the cube) * Time, t = 7200 s * Temperature gradient, dT/dx = 90 °C/m2. Calculate the area (A) of the face: * Since it's a cube, the area of each face is A = side * side = 3 m * 3 m = 9 m²3. Use the formula for heat conduction: * Q = (k * A * dT * t) / x, where: * Q is the heat energy transferred. * k is the thermal conductivity (what we want to find). * A is the area. * dT/dx is the temperature gradient * t is the time. * x is the length4. Rearrange the formula to solve for k: * k = (Q * x) / (A * dT/dx * t)5. Plug in the values and calculate k: * k = (288000 J * 3 m) / (9 m² * 90 °C/m * 7200 s) * k = 864000 / 5832000 * k ≈ 0.05 or 5.0 x 10\(^{-2}\) Wm\(^{-1}\)K\(^{-1}\)

Here's how to solve the problem:The potential difference (emf) is directly proportional to the balancing length in a potentiometer. We can set up a proportion:* E₁ / E₂ = L₁ / L₂Where:* E₁ = 3.06 V* E₂ = 2.295 V* L₁ = 75 cm* L₂ = the unknown balancing lengthNow, plug in the values and solve for L₂:* 3. 06 / 2.295 = 75 / L₂* L₂ = (2.295 * 75) / 3.06* L₂ = 172.125 / 3.06* L₂ = 56.25 cmTherefore, the new balance length is approximately 56.25 cm.

The mechanical advantage (MA) of a machine is calculated as:MA = Output Force / Input Force. However, since the output and input forces are not provided, and from the question it is not clear what kind of machine is shown in the diagram. However, given the options and the nature of JAMB questions, and the fact that the mechanical advantage is a ratio (hence dimensionless), the best approach is to look for any formula that could yield a result from the given options. This question may be interpreted as involving work done, where work done by the machine is equivalent to the effort applied to the machine, therefore the mechanical advantage can be calculated as:MA = (Load * Load Distance) / (Effort * Effort Distance)Given the diagram shows:Load distance = 10 cmEffort distance = 20 cmLoad = 15 NEffort = 5 NMA = (15 N * 20 cm) / (5 N * 10 cm) = 300/10 = 30

Newton's Law of Cooling states that the rate of heat loss of a body is directly proportional to the difference in the temperatures between the body and its surroundings. This law is most accurate when the temperature differences are small. The law becomes less accurate over large temperature ranges because the rate of heat loss doesn't always remain directly proportional to the temperature difference.