Current, potential difference and resistanceIB MYP Sciences: Subtopic test

1. 1
   A technician in Nairobi is testing a small solar-powered lamp. A steady current of 0.50 A flows through the lamp for 2.0 minutes.

   (a)

   Which statement about electric current in a metal wire is correct?

   [1 mark]

   • ACurrent is the flow of atoms along the wire
   • BCurrent is the rate of flow of charge, carried by electrons
   • CCurrent is the energy transferred to each coulomb of charge
   • DCurrent is the opposition to the flow of charge

   (b)

   Calculate the charge that flows through the lamp in this time.

   [1 mark]

   • A0.25 C
   • B1.0 C
   • C60 C
   • D240 C

   (c)

   State where an ammeter and a voltmeter should be connected to measure the current through the lamp and the potential difference across it.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in Seoul connects a fixed resistor to a 6.0 V battery and measures a current of 0.20 A through the resistor.

   (a)

   What does it mean to say that the battery provides a potential difference of 6.0 V?

   [1 mark]

   • AEach coulomb of charge that passes through gains 6.0 J of energy
   • B6.0 coulombs of charge pass through the circuit every second
   • CThe resistor has a resistance of 6.0 Ω
   • DThe battery stores 6.0 A of current

   (b)

   Calculate the resistance of the resistor.

   [1 mark]

   • A1.2 Ω
   • B0.033 Ω
   • C5.8 Ω
   • D30 Ω

   (c)

   The student replaces the resistor with one of twice the resistance and keeps the same battery. Calculate the new current.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A greenhouse controller in Almería, Spain, uses a thermistor to monitor the air temperature and a light-dependent resistor (LDR) to monitor daylight. Each sensor is connected to a constant 3.0 V supply.

   (a)

   Describe how the resistance of the thermistor changes as the greenhouse warms up, explain the effect on the current in its circuit, and suggest how the controller could use this change.

   [3 marks]

   (b)

   In a test, the LDR circuit gives a current of 0.030 A in bright daylight and 0.0030 A at dusk. Calculate the resistance of the LDR in each case and describe the trend in resistance as the light level falls.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A small company in Nairobi is developing a low-cost electric cooker that heats food using a coil of nichrome wire. Its engineers must choose the length of wire to use. The company also hopes that households will use the cooker instead of cooking over charcoal.

   (a)

   Design a safe investigation to find how the length of nichrome wire affects its resistance. State the variables and the measurements you would take.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of households using electric cookers instead of charcoal, and reach a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions