ElectromagnetismIB MYP Sciences: Topic test

1. 1
   A metal-cased heater in a hostel in Kathmandu is rated at 1.0 kW. It is connected to the 230 V mains supply by a three-core cable and a plug that contains a fuse.

   (a)

   Which wire in the cable is connected to the metal casing of the heater?

   [1 mark]

   • AEarth wire
   • BLive wire
   • CNeutral wire
   • DBoth the live wire and the neutral wire

   (b)

   Which fuse is the most suitable for the plug of this heater?

   [1 mark]

   • A1 A
   • B3 A
   • C5 A
   • D13 A

   (c)

   Explain how the earth wire and the fuse together protect a user if the live wire comes loose and touches the metal casing.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in Oslo connects a 6.0 V battery, a 10 Ω resistor and a 20 Ω resistor in series.

   (a)

   What is the total resistance of the circuit?

   [1 mark]

   • A6.7 Ω
   • B30 Ω
   • C200 Ω
   • D10 Ω

   (b)

   How does the current through the 10 Ω resistor compare with the current through the 20 Ω resistor?

   [1 mark]

   • AIt is twice as large
   • BIt is half as large
   • CIt is one third as large
   • DIt is the same

   (c)

   Calculate the potential difference across the 20 Ω resistor.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An electric shower in a flat in Istanbul is rated at 8.0 kW and works from the 230 V mains supply. A family uses the shower for 10 minutes each day. Electricity costs 0.12 USD for each kilowatt-hour (kWh).

   (a)

   Calculate the current in the shower when it is working normally.

   [3 marks]

   (b)

   Calculate the cost of using the shower for 30 days.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A scrapyard in Rotterdam wants to replace a diesel-powered crane with an electric crane that lifts scrap steel using a large electromagnet. Engineers first test small electromagnets in a laboratory. Each is an iron nail wound with insulated copper wire and connected to a variable d.c. power supply. The strength of an electromagnet can be compared by counting how many steel paper clips it picks up.

   (a)

   Design an investigation to find out how the number of turns of wire affects the strength of the electromagnet. Include a hypothesis with a reason, the variables and a safety precaution.

   [6 marks]

   (b)

   Discuss the advantages and disadvantages of replacing the diesel crane with the electromagnet crane. Give a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A student in Kyoto places a sheet of card over a bar magnet and sprinkles iron filings on it. After she taps the card, the filings settle into a pattern of curved lines.

   (a)

   Where are the iron filings most closely packed together?

   [1 mark]

   • AHalfway along the side of the magnet
   • BNear the poles at the ends of the magnet
   • CFar from the magnet
   • DAlong the edges of the card

   (b)

   She now brings the north pole of a second bar magnet close to the north pole of the first magnet. What happens?

   [1 mark]

   • AThe magnets repel each other
   • BThe magnets attract each other
   • CThere is no force between them
   • DThe first magnet loses its magnetism

   (c)

   Describe how a plotting compass could be used instead of iron filings to show the direction of a magnetic field line around the magnet.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A student in Medellín investigates a light-dependent resistor (LDR). The LDR is connected in series with a fixed resistor, an ammeter and a 6.0 V battery, and a voltmeter is connected across the LDR. In bright light the ammeter reads 0.030 A and the voltmeter reads 3.0 V. In a dark cupboard the ammeter reads 0.0050 A and the voltmeter reads 5.5 V.

   (a)

   What is the resistance of the LDR in bright light?

   [1 mark]

   • A0.010 Ω
   • B0.090 Ω
   • C100 Ω
   • D200 Ω

   (b)

   Which statement about the LDR is correct?

   [1 mark]

   • AIts resistance decreases as the light gets dimmer
   • BIts resistance stays the same in all conditions
   • CIts resistance only changes when the current changes
   • DIts resistance increases as the light gets dimmer

   (c)

   Calculate the resistance of the LDR in the dark and compare it with its resistance in bright light.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A student in Kampala connects two lamps in parallel to a 12 V battery. Lamp P has a resistance of 24 Ω and lamp Q has a resistance of 8.0 Ω. Assume the wires have no resistance.

   (a)

   Calculate the current through each lamp.

   [3 marks]

   (b)

   Calculate the total energy transferred by the battery to the two lamps in 5.0 minutes.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A farm in Denmark has a small wind turbine that turns a generator. A group of students build a model generator: a coil of insulated wire on an axle that is turned by hand between two magnets and connected to a voltmeter. They turn the axle at three speeds and record the largest reading each time: slow turning gives 0.4 V, medium turning gives 0.9 V and fast turning gives 1.9 V. They tried each speed once and judged the speeds by eye.

   (a)

   Explain how the generator in the wind turbine produces an electric current, and describe two ways of increasing the potential difference it produces.

   [6 marks]

   (b)

   Evaluate the students' conclusion that faster turning gives a larger potential difference, and suggest two improvements to their method.

   [6 marks]

   Total for question 8: 12 marks

End of questions