Explain what an ultrasound wave is (2 marks) 2) Ultrasound waves can be used to clean jewellery. One method is to put the jewellery in a bath of cleaning fluid which contains an electronic oscillator. The electronic oscillator generates ultrasound waves in the cleaning fluid. Suggest how these waves clean the jewellery (2 marks)

Explain what an ultrasound wave is (2 marks) sound / mechanical / longitudinal (wave ) (1) any one from: • above 20 000 hertz / 20kHz • above (human) audible range • cannot be heard by humans

2) Suggest how these waves clean the jewellery (2 marks) either particles / molecules / fluid vibrate(s) (1) (and) knock particles of dirt off the jewellery (1) or by the process of cavitation (1) which breaks up / releases dirt from the surface (1)

Electromagnetic induction L.O. Design an alternating current generator. Explain how to increase the induced potential difference in a generator. Homework due on 11th February: workbook pages 130 & 131.

Simulation

In the pairs: describe how the electromagnetic induction takes place and how to increase it. Key words: magnetic field lines, induced voltage, alternating current.

How to generate electricity. Watch clip and fill in gaps in script

Task: design an AC generator Make some drawings of your design. Explain how an electric potential difference is induced. Consider how you could increase the induced potential difference.

7.a) (magnetic) field / lines of force / flux rotate(s) / move(s) / through / in / cut(s) the coil (1 mark) potential difference / p.d. / voltage induced across the coil (mark)

7b) any one from: • more powerful / stronger / lighter magnet • larger / more / bigger / lighter cups / with a bigger surface area • longer arms • lubricate the spindle • add more turns to the coil

(a) (i) (electromagnetic) induction (1) 1(ii) swings to the left (1) 1(iii) no (induced) current (1)

6a) increase the current (1) increase the magnetic field (strength) (1) 6b) either reverse polarity or connect the battery the other way round. (1) either reverse direction of the magnetic field or put the magnet the other way round / reverse the magnet (1)

Electromagnetic induction L.O. Design an alternating current generator. Explain how to increase the induced potential difference in a generator.

Electromagnetic Induction

Electromagnetic Induction

Electromagnetic Induction

Electromagnetic Induction

Increasing the voltage

How to generate electricity clip

Task: Workbook pages 130-131.