Recall that different substances may absorb, transmit, refract, or reflect…

The idea

When an electromagnetic wave meets a substance, one or more things happen: the substance absorbs the wave, transmits it through, refracts it as it changes speed at a boundary, or reflects it at a surface. The key Higher-tier idea is that how strongly each of these occurs depends on the wavelength of the wave, not just on the substance. A familiar example is a glass window: it transmits visible light well, yet absorbs much of the ultraviolet beyond the visible range and blocks some infrared. A coloured filter absorbs some visible wavelengths and transmits others, which is why it looks coloured. A shiny metal surface reflects a broad range of wavelengths, while a radio aerial responds to long wavelengths.

What earns the marks

• Identifies absorption as the transfer of electromagnetic wave energy into a substance, often raising its temperature.
• Recognises transmission as electromagnetic waves passing through a substance rather than being absorbed or reflected.
• Describes refraction as the change in direction of electromagnetic waves when their velocity changes on entering a different substance.
• States that reflection occurs when electromagnetic waves bounce off a surface or boundary.
• Explains that the extent of absorption, transmission, refraction or reflection depends on the wavelength of the electromagnetic wave.
• Selects the option that correctly links a named process to a wavelength-dependent example, such as a filter transmitting some visible wavelengths and absorbing others.

Common mistakes and how to put them right

• Confuses refraction with reflection.

  Put it right: Keep refraction as a change of direction caused by a change of velocity inside a new substance, and reflection as bouncing off a surface.

• Assumes a substance treats all wavelengths identically.

  Put it right: Recognise that absorption, transmission, refraction and reflection all vary with wavelength.

• Treats transmission as the wave being absorbed and re-emitted.

  Put it right: Describe transmission as the wave passing through the substance.

• Ignores the wavelength clause and picks an option that is only about the substance.

  Put it right: Check that the chosen option mentions how the effect varies with wavelength.

Exam tips

• Read each option and underline the named process (absorb, transmit, refract, reflect); eliminate any option that describes the wrong process.
• Check the wavelength clause: a correct option must show the effect changing with wavelength, not just with the substance.
• Use a concrete example such as a coloured filter or a glass window to test whether an option makes physical sense before selecting it.