Form 5 Physics Bab 4: Electromagnetism
Instructions
Answer all structured questions. Show clear working for numerical problems and state principles where required.
10 questions · 26 marks total
1. True or False: In a step-up transformer, the secondary winding current is lower than the primary winding current assuming high efficiency.
True / False · 1m2. A transformer steps down 240 V a.c. to 12 V a.c. to operate a 24 W lamp. The primary current drawn from the mains is 0.125 A. (a) Calculate the input electrical power to the primary coil. (b) Calculate the efficiency of the transformer.
Short Answer · 3m3. True or False: A transformer can be used to step up or step down the voltage of a constant direct current (d.c.) power supply.
True / False · 1m4. Fill in the blank: The rule used to determine the direction of induced current in a generator is Fleming's ________-Hand Rule.
Fill in the Blank · 1m5. A power generator supplies 100 kW of electrical power to a distant town through transmission cables of total resistance 2.0 Ω. (a) Calculate the power loss in the cables if transmitted at 2000 V. (b) Calculate the power loss in the cables if transmitted at 20,000 V. (c) Based on your answers, explain why high-voltage transmission is essential in the National Grid.
Short Answer · 5m6. A simple direct current (d.c.) motor consists of a rectangular armature coil in a magnetic field. (a) State two methods to reverse the direction of rotation of the motor. (b) State two modifications that can increase the turning torque of the motor coil.
Short Answer · 4m7. A transformer connected to a 240 V a.c. supply has 1200 turns on its primary coil and 60 turns on its secondary coil. (a) Calculate the secondary output voltage. (b) State whether this is a step-up or step-down transformer. (c) If the secondary coil delivers 2.0 A to a lamp with 100% efficiency, calculate the current in the primary coil.
Short Answer · 4m8. A bar magnet is dropped vertically through a vertical hollow copper tube. (a) Explain why the acceleration of the falling bar magnet is LESS than acceleration due to gravity (g). (b) State the physics law that explains this observation.
Short Answer · 3m9. Which structural modification reduces power loss caused by eddy currents in the core of a transformer?
Multiple Choice · 1m10. A horizontal copper rod of length 0.25 m carrying a current of 3.0 A is placed at right angles to a uniform magnetic field of magnetic flux density 0.40 T. (a) Name the rule used to find the force direction. (b) Calculate the magnitude of the magnetic force acting on the rod.
Short Answer · 3m