An electron microscope has much higher magnification and resolving power…

The idea

Magnification tells you how many times larger an image appears than the object; resolving power is the smallest separation at which two points can still be seen as separate. A light microscope uses visible light, whose relatively long wavelength limits resolution to roughly 200 nm, so its useful magnification is capped at about ×1500. An electron microscope uses a beam of electrons with a far shorter wavelength, giving resolution down to about 0.2 nm and magnifications of ×500 000 or more. For example, a mitochondrion about 1 µm long appears roughly 1 mm across at ×1000, but an electron micrograph can enlarge the same organelle until its internal cristae are distinguishable. Higher resolving power, not magnification alone, is what reveals fine detail.

What earns the marks

• Magnification is the number of times an image is larger than the real object; resolving power is the ability to distinguish two separate points as distinct.
• Light microscopes use visible light with a relatively long wavelength, limiting resolution to about 200 nm and useful magnification to roughly ×1500.
• Electron microscopes use a beam of electrons with a much shorter wavelength, giving resolution near 0.2 nm and far greater magnification.
• Because resolution is better, electron microscopes reveal detail that light microscopes blur into a single point, even if the light image is enlarged further.
• Calculations such as magnification = image size ÷ actual size apply to images from either microscope.

Common mistakes and how to put them right

• Confusing magnification with resolving power.

  Put it right: Magnification enlarges an image, whereas resolving power determines whether fine detail remains distinguishable; state both definitions separately.

• Believing that simply enlarging a light microscope image reveals more detail.

  Put it right: Beyond the resolution limit the image only becomes blurrier, so detail is not gained.

• Thinking electron microscopes use light or lenses in the same way as light microscopes.

  Put it right: They use a beam of electrons focused by electromagnets, and specimens must be dead and in a vacuum.

Exam tips

• Define both terms before comparing, then link the comparison to wavelength of light versus electrons.
• Use comparative wording such as 'much higher' or 'far greater' when the question asks for a comparison.
• If asked to calculate magnification, rearrange magnification = image size ÷ actual size carefully and give units, converting µm to mm where needed.