An engineer tests a fabric sample intended for use in a thermal blanket. Two beams of radiation, each with a single wavelength, are directed at the fabric. The table shows the energy incident on the fabric and the energy transmitted and reflected at each wavelength.
| Wavelength | Energy incident | Energy transmitted | Energy reflected |
|---|---|---|---|
| 610 nm610\ \mathrm{nm}610 nm | 150 J | 45 J | 30 J |
| 2.5 μm2.5\ \mu\mathrm{m}2.5 μm | 250 J | 75 J | 25 J |
Which gives the percentage of the incident energy that the fabric absorbs at each wavelength?
At 610 nm610\ \mathrm{nm}610 nm: 50%50\%50%. At 2.5 μm2.5\ \mu\mathrm{m}2.5 μm: 40%40\%40%.
At 610 nm610\ \mathrm{nm}610 nm: 50%50\%50%. At 2.5 μm2.5\ \mu\mathrm{m}2.5 μm: 60%60\%60%.
At 610 nm610\ \mathrm{nm}610 nm: 70%70\%70%. At 2.5 μm2.5\ \mu\mathrm{m}2.5 μm: 70%70\%70%.
At 610 nm610\ \mathrm{nm}610 nm: 20%20\%20%. At 2.5 μm2.5\ \mu\mathrm{m}2.5 μm: 10%10\%10%.
84 exam-style questions on Edexcel GCSE Physics 5.2 The electromagnetic spectrum, covering 5.2.1 Electromagnetic waves and refraction in glass (core practical), 5.2.2 Groups of the electromagnetic spectrum, 5.2.3 Wavelength-dependent behaviour of EM waves, and 5.2.4 Velocities of EM waves in different substances. Each one has a worked solution and a mark scheme showing where the marks go.