This question is about microwave ovens and microwaves.
(a) A microwave oven cooks some food. Diagram 1 represents a microwave emitted by the microwave oven.
(i) Determine the wavelength of the microwave. (2)
(ii) The microwave has a frequency of \(2.35\,\mathrm{GHz}\). Show that the speed of the microwave is about \(3\times10^8\,\mathrm{m\,s^{-1}}\). (3)
(b) Diagram 2 shows a damaged microwave oven with a hole in the door.
This microwave oven should not be used as it is very dangerous. State a harmful effect from the microwaves if this oven is used. (1)
Syllabus Topic Codes (Edexcel International GCSE Physics 4PH1):
(a)(i) Wavelength of the microwave [2 marks]
Measure the horizontal distance between two adjacent points in phase, such as two successive crests.
From the diagram, the wavelength is approximately:
\(\lambda\approx12.5\,\mathrm{cm}\)
Therefore:
\(\boxed{\lambda=12.5\,\mathrm{cm}}\)
(a)(ii) Speed of the microwave [3 marks]
Use the wave equation:
\(v=f\lambda\)
Convert the units:
\(f=2.35\,\mathrm{GHz}=2.35\times10^9\,\mathrm{Hz}\)
\(\lambda=12.5\,\mathrm{cm}=12.5\times10^{-2}\,\mathrm{m}\)
Substituting:
\(v=(2.35\times10^9)(12.5\times10^{-2})\)
\(v=2.9375\times10^8\,\mathrm{m\,s^{-1}}\)
To an appropriate number of significant figures:
\(\boxed{v\approx3.0\times10^8\,\mathrm{m\,s^{-1}}}\)
(b) Harmful effect of microwaves [1 mark]
Microwaves can cause internal heating of body tissues or organs.
Therefore, leakage of microwaves from a damaged oven could cause harmful heating of the body.
