Magnetism and magnetic forces - Section B - Six-mark questions

Six-mark questions are extended open response questions. These require longer answers than the structured questions with fewer marks. It is wise to plan your answer rather than rushing straight into it, otherwise you may stray away from the key points.

Six-mark questions are marked using a levels-based mark scheme because they are open ended. To gain full marks, you need to:

  • support explanations using scientific knowledge and understanding
  • use appropriate scientific words and terms
  • write clearly, linking ideas in a logical way
  • maintain a sustained line of reasoning, rather than getting lost or bogged down

You are likely to see command words such as:

  • 'describe' - you need to give an account but no reason
  • 'explain' - you must give reasons or explanations
  • 'devise' - you must plan or invent a procedure using your scientific knowledge and understanding
  • 'evaluate' - you must review information, including identifying strengths and weaknesses, and make a supported conclusion

Six-mark questions may be synoptic questions. These questions bring together ideas from two or more topics. For example, a question about atoms could include ideas about atomic structure, isotopes, radiation and nuclear reactions.

Remember that the topics covered in the first paper are assumed knowledge for the second paper, so questions in the second paper may need knowledge and understanding of those topics too.

The answers shown here give marking points as bullet points. You do not usually need to include all of them to gain six marks, but you do need to write in full sentences, linking them logically and clearly.

Sample question 1 - Foundation

Question

The Earth is surrounded by a magnetic field. Explain how the behaviour of a magnetic compass is related to evidence that the core of the Earth must be magnetic.

In your answer, describe how the field is detected, what causes it and where the poles are. [6 marks]

This question has been written by a Bitesize consultant as a suggestion to the type of question that may appear in an exam paper.

The core of the Earth is molten iron. Molten iron moving in the core causes the magnetic field. The Earth has north and south magnetic poles. The needle of the compass follows the magnetic field lines. The N pole of the magnet points to the North Pole of the Earth and the S pole of the magnet points to the South Pole. Opposite magnetic poles attract. So the North Pole must be the south pole of the Earth's magnetic field and the South Pole must be the north pole of the Earth's magnetic field. A dipping compass points downwards and follows the magnetic field lines.

Answering tip: Briefly plan the key points you want to include in your answer. For example:

  • what the core is made from and how it makes the field
  • use of a magnet/compass to detect the field
  • explain the poles

Sample question 2 - Foundation

Question

A magnetic field forms when an electric current flows through a straight piece of insulated wire. The magnetic effect is enhanced when this wire is made into a coil.

Describe the direction of the magnetic field around the straight wire, and how this can be determined. Describe how the magnetic effect of the coiled wire can be increased. [6 marks]

This question has been written by a Bitesize consultant as a suggestion to the type of question that may appear in an exam paper.

The magnetic field is circular around the wire / at right angles to the length of the wire. To detect the magnetic field, push the wire through a hole in a piece of paper. Make sure the wire is kept perpendicular to the paper. Sprinkle iron filings on the paper or use a plotting compass to detect the magnetic field.

The magnetic effect of the coil is increased if there is an increase in:

  • the current
  • the length of the wire
  • the number of turns
  • the cross-sectional area

Answering tip: Briefly plan the key points you want to include in your answer. For example:

  • shape/direction of the field
  • iron filings or compass to detect the field
  • factors affecting strength of the field

Sample question 3 - Higher

Question

This question is about transformers.

Look at the information about two different transformers.

Transformer ATransformer B
Type of coreIronIron
Number of primary turns5001,000
Number of secondary turns1,000500
Input voltage20 V ac20 V ac

Compare and contrast the characteristics of the two transformers. Include information about their construction, output voltage and uses. [6 marks]

OCR Gateway Science, GCE Physics, Paper B752, June 2014 - Higher.

Both of the transformers have an iron core and the same number of turns on the primary coils compared to the secondary coils. They also have the same input voltage (20 volts ac). The input voltage is connected to the primary coil and the output voltage is connected to the secondary coil. However, transformer A has fewer turns on the primary coil than transformer B. Transformer A has more turns on the secondary coil than transformer B.

Both of the transformers change the output voltage. Transformer A is a step-up transformer and transformer B is a step-down transformer. The output of transformer A will be 40 V and the output of transformer B will be 10 V.

The transformers have different uses. Transformer A is used in the National Grid and in TVs. Transformer B is used in mobile phone chargers, radios, laptops, the National Grid (to decrease voltage) and in any electronic device that is mains powered, eg halogen lights.

Answering tip: Briefly plan the key points you want to include in your answer. For example:

  • what is the same (construction and output)
  • what is different (and whether step-up or step-down)
  • uses of each one

Sample question 4 - Higher

Question

Wendy's mobile phone charger contains a transformer.

Look at the information about the transformer.

Input voltage230 V ac
Input current50 mA
Output voltage5 V

Describe, in detail, the construction of the transformer and explain how applying a 230 V input produces a 5 V output. Include a calculation in your answer. [6 marks]

OCR Gateway Science, GCE Physics, Paper B752, June 2013 - Higher.

Transformers are constructed from two coils of wire wrapped on an iron core. Step-down transformers have fewer turns on the secondary coil than on the primary coil. To convert 230 V to 5 V the ratio of the turns should be 230:5 or 2%.

Calculations:

230 ÷ 5 = 46 × more turns on primary coil

output current = 46 × input current

output current = 46 × 50 = 2,300 mA

Answering tip: Briefly plan the key points you want to include in your answer. For example:

  • key parts of the transformer
  • use voltages to calculate the relative number of turns
  • why ac is needed - magnetic field