CIE iGCSE Co-Ordinated Science P4.4 Electrical safety Exam Style Questions Paper 3
Question
Fig. 9.1 shows an aircraft at rest on a runway.
(a) The mass of the aircraft is 400 000 kg.
Calculate the weight of the aircraft. The gravitational field strength, \( g \), is 10 N/kg. (Topic – P1.3)
▶️Answer/Explanation
Weight = 4,000,000 N
Explanation: Weight is calculated using the formula \( W = m \times g \), where \( m \) is mass and \( g \) is gravitational field strength. Substituting the values, \( W = 400,000 \, \text{kg} \times 10 \, \text{N/kg} = 4,000,000 \, \text{N} \).
(b) The aircraft starts from rest and accelerates along the straight runway. The aircraft engines produce a constant horizontal thrust force of 1,200,000 N. A constant frictional force of 500,000 N acts on the aircraft. (Topic – P1.5)
(i) Calculate the resultant horizontal force acting on the aircraft.
▶️Answer/Explanation
Resultant force = 700,000 N
Explanation: The resultant force is calculated by subtracting the frictional force from the thrust force: \( F_{\text{resultant}} = 1,200,000 \, \text{N} – 500,000 \, \text{N} = 700,000 \, \text{N} \).
(ii) Explain why the aircraft accelerates.
▶️Answer/Explanation
The aircraft accelerates because there is a resultant force acting on it.
Explanation: According to Newton’s Second Law of Motion, an object accelerates when there is a resultant force acting on it. In this case, the resultant force of 700,000 N causes the aircraft to accelerate.
(c) Fig. 9.2 shows a TV monitor in the cabin of the aircraft and the energy transferred each second by the monitor.
(i) The number of joules of sound energy transferred per second is shown as XJ. Calculate the value of X. (Topic – P1.6)
▶️Answer/Explanation
X = 1 J
Explanation: The total energy input is 200 J, and the energy outputs are 119 J (light) and 80 J (thermal). Therefore, the sound energy \( X = 200 \, \text{J} – (119 \, \text{J} + 80 \, \text{J}) = 1 \, \text{J} \).
(ii) The monitor has a resistance of 1900 Ω. The current passing through the monitor when in use is 0.060 A.
Calculate the potential difference across the monitor. State the unit of your answer. (Topic – P4.2)
▶️Answer/Explanation
Potential difference = 114 V
Explanation: The potential difference (V) is calculated using Ohm’s Law: \( V = I \times R \). Substituting the values, \( V = 0.060 \, \text{A} \times 1900 \, \Omega = 114 \, \text{V} \).
(iii) The current of 0.060 A is the same as 60 mA. The fuse in the electrical supply to the monitor has to be replaced. Several fuse ratings are available.
10 mA 50 mA 100 mA 250 mA
State which fuse is the correct choice. Explain your answer. (Topic – P4.4)
▶️Answer/Explanation
Fuse = 100 mA
Explanation: The fuse rating should be higher than the maximum current (60 mA) but not too much higher to ensure safety. A 100 mA fuse is the most appropriate choice as it is the smallest value above 60 mA.