CIE iGCSE Co-Ordinated Science P1.6.4 Power Exam Style Questions Paper 4
Question
(a) Fig. 12.1 shows a gardener using a leaf-blower.
Fig. 12.2 shows the energy input and outputs for the leaf-blower.
Calculate the efficiency of the leaf-blower as a percentage. Show your working.
▶️Answer/Explanation
Answer: 37.5%
Working:
Efficiency = (useful energy output ÷ total energy input) × 100
= (3 ÷ 8) × 100
= 37.5%
Explanation:
- Efficiency measures how much input energy is converted to useful output
- Always expressed as percentage (0-100%)
- Typical leaf blowers are 30-40% efficient due to:
- Air resistance
- Motor heat losses
- Sound energy
- Vibration
(b) When used the leaf-blower takes a current of 3.0A.
Calculate the charge that flows through the leaf-blower when it is used for 180 seconds. Show your working.
▶️Answer/Explanation
Answer: 540 C
Working:
Charge (Q) = Current (I) × Time (t)
= 3.0 A × 180 s
= 540 C
Explanation:
- 1 Coulomb = 1 Amp × 1 second
- This equals ≈3.36×10²¹ electrons flowing
- Practical implications:
- Higher current or longer use → more charge transferred
- Battery capacity often rated in Amp-hours (1 Ah = 3600 C)
(c) The leaf-blower contains a small electric motor powered by a battery.
Fig. 12.3 shows a simple electric motor powered by a battery.
(i) State the name of the component labelled Q on Fig. 12.3.
▶️Answer/Explanation
Answer: split ring commutator
Explanation:
- Function:
- Reverses current direction every half-rotation
- Maintains unidirectional torque
- Construction:
- Two semicircular copper segments
- Insulated from each other
- Connects to coil via brushes
- Differs from slip rings (AC motors)
(ii) Draw an arrow on Fig. 12.3 to show the direction of the magnetic field.
▶️Answer/Explanation
Answer: Arrow from N pole to S pole of permanent magnet
Explanation:
- Magnetic field lines:
- Exit North pole, enter South pole
- Continuous loops through magnet
- Right-hand rule:
- Thumb points N→S outside magnet
- Fingers show field direction
- Affects motor rotation direction (Fleming’s Left Hand Rule)
(iii) Explain why the coil moves when an electric current passes through it.
▶️Answer/Explanation
Answer:
Current creates magnetic field around coil
Interaction with permanent magnet’s field
Force acts on current-carrying conductor (Fleming’s Left Hand Rule)
Explanation:
- Motor effect: Charged particles moving in magnetic field experience force
- Field interaction:
- Coil field is circular (right-hand grip rule)
- Permanent magnet field is N→S
- Resultant field causes attraction/repulsion
- Force calculation: F = BILsinθ
- B = magnetic flux density
- I = current
- L = conductor length