1. 1
   A technician sets up a straight length of copper wire connected to a battery so that a current flows through it, and investigates how reshaping the wire changes the strength of the magnetic effect around it. She then adds an iron core inside a coiled section of wire.

   (a)

   What is produced in the space around the wire as a result of the current?

   [1 mark]

   • AAn electric field only
   • BA magnetic field
   • CA gravitational field
   • DNo field is produced unless the wire is coiled

   (b)

   The technician then reshapes the same length of wire into a tightly wound coil (a solenoid) carrying the same current. What effect does this have on the magnetic field compared with the straight wire?

   [1 mark]

   • AThe magnetic field strength is unchanged
   • BThe magnetic field disappears completely
   • CThe magnetic field strength is increased
   • DThe magnetic field strength is reduced to zero at the coil's centre

   (c)

   The technician then places an iron core inside the solenoid. Explain the effect this has, and describe how the resulting magnetic field pattern differs from that of the straight wire.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   On a factory conveyor system, an electric motor uses a coil of wire carrying a current, placed inside a magnetic field, to produce rotation and keep the conveyor belt moving. Engineers want to increase the force produced on one straight section of the coil, which currently carries a current of 2 A through a magnetic field of flux density 0.5 T, over a length of 0.4 m within the field.

   (a)

   Which rule can be used to find the relative directions of the force, current and magnetic field for this coil?

   [1 mark]

   • AFleming's left-hand rule
   • BNewton's third law
   • CLenz's law
   • DThe right-hand grip rule for a solenoid

   (b)

   (HT) Which of the following, if increased on its own, would increase the size of the force on the current-carrying section of the coil described above?

   [1 mark]

   • ADecreasing the magnetic flux density of the field
   • BIncreasing the resistance of the coil's insulation
   • CIncreasing the distance between the coil and the motor's magnets
   • DIncreasing the current flowing through the coil

   (c)

   (HT) Calculate the force on the section of the coil described above, given a current of 2 A, a magnetic flux density of 0.5 T, and a length within the field of 0.4 m. Use F = BIl.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A pair of headphones converts an electrical audio signal into sound using a moving-coil speaker inside each earpiece. A musician also uses a moving-coil microphone, built in a similar way, to record their singing voice.

   (a)

   Explain how a moving-coil headphone speaker uses the motor effect to convert variations in current into pressure variations in sound waves.

   [3 marks]

   (b)

   (HT) The musician's moving-coil microphone works in essentially the opposite way to the headphone speaker. Explain how the microphone uses the generator effect to convert the pressure variations of the musician's voice into a varying electrical current.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A power station generates electricity and transmits it hundreds of kilometres across the National Grid to towns and cities, using step-up transformers near the power station and step-down transformers near consumers, before a final step-down transformer reduces the potential difference to a safe level for homes.

   (a)

   (HT) A step-up transformer has 200 turns on its primary coil and 4000 turns on its secondary coil, and the primary coil is supplied with a potential difference of 25,000 V. Explain how a transformer works, and calculate the potential difference produced across the secondary coil.

   [6 marks]

   (b)

   (HT) Explain the advantages of transmitting electrical power across the National Grid at a very high potential difference (as produced by the step-up transformer), rather than transmitting it at the lower potential difference generated at the power station.

   [6 marks]

   Total for question 4: 12 marks

End of questions