2025 WAEC GCE FIRST Series Physics Questions and Answers

(1a)
Kgm²s⁻¹
This unit represents angular momentum or moment of inertia.

(1b)
Kgm⁻¹s⁻²
This unit represents pressure or stress.

(1c)
Kgs⁻²
This unit represents force or weight.

(2)
Wear appropriate eye protection: Laser radiation can be harmful to the eyes. Use laser safety eyewear designed for the specific wavelength and power of the laser.
Never look directly into the laser beam: Even a brief exposure can cause serious eye damage.
Ensure the laser is properly labeled and operated: Follow safety protocols and training when operating lasers. Make sure the laser is in a controlled environment to prevent accidental exposure to others.

(3)
Calculate the compression distance (x):
x = Original length – Compressed length
x = 25 cm – 10 cm = 15 cm = 0.15 meters (Convert to meters)
Use the work done formula for a spring:
Work done (W) = (1/2)kx² , where k is the spring constant.
Rearrange the formula to solve for k:
k = 2W / x²
k = (2 * 15 J) / (0.15 m)²
k = 30 / 0.0225 = 1333.33 N/m (approximately)
Use Hooke’s Law to find the force (F):
F = kx
F = (1333.33 N/m) * (0.15 m)
F = 200 N
Therefore, the magnitude of force F is 200 Newtons.

(4)
Conductors: Materials that allow electric current to flow freely (e.g., copper, aluminum, silver, gold).
Semiconductors: Materials with conductivity between that of a conductor and an insulator (e.g., silicon, germanium). Conductivity can be controlled by adding impurities (doping) or by applying external electric fields.
Insulators: Materials that do not allow electric current to flow (e.g., rubber, glass, plastic, wood).

(5)
Find the vertical component of the initial velocity (v_y):
v_y = v * sin(θ)
v_y = 20 m/s * sin(30°)
v_y = 20 m/s * 0.5 = 10 m/s
Use the following kinematic equation to find the maximum height (H):
v_f² = v_i² + 2as
Where:
v_f = 0 m/s (final velocity at the maximum height)
v_i = 10 m/s (initial vertical velocity)
a = -10 m/s² (acceleration due to gravity, negative since it’s opposing the motion)
s = H (the maximum height we want to find)
Rearrange and solve for H:
0 = (10 m/s)² + 2*(-10 m/s²)*H
0 = 100 – 20H
20H = 100
H = 100 / 20
H = 5 meters

(9ai)
A thermometric substance is a material that changes its physical properties, such as volume or electrical resistance, in response to changes in temperature. Examples include mercury, alcohol, and thermistors.

(9aii)
(i)Mercury
(ii)Alcohol

(9b)
°C to °F conversion formula: °F = (°C × 9/5) + 32
°F = (38.5 × 9/5) + 32
= 101.3 °F

(9c)
The kinetic theory of matter states that particles in a substance are in constant motion. When the balloon was left in the sun, the particles inside the balloon gained kinetic energy and started moving faster. This increased the pressure inside the balloon, causing it to expand and eventually burst.

(9di)
Charles’ Law states that, at constant pressure, the volume of a gas is directly proportional to the temperature in Kelvin.

(9dii)
The relationship is: V1 / T1 = V2 / T2

(9diii)
Given: P1 = 800 mmHg, T1 = 186°C + 273 = 459 K, P2 = 1020 mmHg
Using the combined gas law: P1V1 / T1 = P2V2 / T2
Since the volume is constant, V1 = V2.
Rearranging the equation to solve for T2: T2 = P2T1 / P1
= (1020 mmHg × 459 K) / 800 mmHg
= 586.5 K
Converting back to Celsius: T2 = 586.5 K – 273 = 313.5°C

(11ai)
A magnetic material is a substance that is capable of being magnetized, meaning it can be influenced by a magnetic field and exhibit magnetic properties.

(11aii)
(i)Electrical method: wrapping a coil of wire around a core and passing an electric current through it.

(ii)Permanent magnet method: heating and cooling a ferromagnetic material in the presence of a magnetic field.

(11aiii)
Iron
Nickel

(11b)
To calculate impedance, we use the formula: Z = √(R^2 + Xc^2), where Xc = 1 / (2πfC).
First, we need to calculate Xc. Given C = 20μF and f = 100Hz, we can plug in the values:
Xc = 1 / (2π * 100Hz * 20μF) = 1 / (0.01256) = 79.58 ohms.
Now we can calculate impedance:
Z = √(R^2 + Xc^2) = √(100^2 + 79.58^2) = √(10000 + 6333) = √16333 = 127.8 ohms.

(ii)
The magnitude of the circuit is the impedance, which we already calculated: 127.8 ohms.

(iii)
To calculate the potential across the capacitor, we use the formula: Vc = I * Xc, where I is the current.
First, we need to calculate the current using Ohm’s law: I = V / Z, where V is the voltage.
Given V = 120V and Z = 127.8 ohms, we can plug in the values:
I = 120V / 127.8 ohms = 0.938A.
Now we can calculate the potential across the capacitor:
Vc = I * Xc = 0.938A * 79.58 ohms = 74.67V.

(11ci)
An electric line of force, also known as an electric field line, is an imaginary line that emerges from a positive charge and enters a negative charge, representing the direction of the electric field at various points in space.

(12ai)
The decay constant (λ) is the probability of decay per unit time.

(12aii)
λ = -ln(N(t)/N0) / t
= -ln(1/4) / 1
= 0.693 per hour

(12b)
t = -ln(N(t)/N0) / λ
= -ln(30/38) / 0.000124
≈ 1750 years

(12ci)
Mass defect = Total mass of protons and neutrons – Nuclear mass
= (8 * 1.007825 + 8 * 1.008665) – 15.99491
≈ 0.13701 amu

(12cii)
Binding energy = Mass defect * 931 MeV/amu
≈ 0.13701 * 931
≈ 127.5 MeV

(12d)
(i)Radiation exposure
(ii)Genetic damage
(iii)Cancer risk
(iv)Tissue damage