Loading…
Loading…
GCSE Physics · key term
The distance from the optical centre of a lens to a principal focus.
Used by AQA, Edexcel and OCR
Specification 4.6.2.5 · Paper 2
The distance along the principal axis from the centre of a lens to its principal focus.
Revise: LensesIf the object is farther from the lens than the focal length, the two rays meet on the far side. Their crossing marks the tip of a real image: draw an image arrow from the axis to that point. The image is inverted and can be caught on a screen.
Specification 5.4P, 5.5P, 5.6P · Paper 1
The distance from the centre of a lens to its principal focus, represented by and measured in metres when calculating lens power.
Revise: Lens PowerA lens that changes the direction of light strongly brings rays together—or spreads them out—over a shorter distance, so it has a shorter focal length. A weak lens produces a smaller change in direction and has a longer focal length.
The distance from the centre of a lens to its principal focus, represented by .
Paper 1, Paper 2
The distance from the optical centre of a lens to its principal focus.
Revise: Reflection, Refraction and LensesThat distance is the focal length.
Convert focal length to metres before using ; using centimetres gives the wrong numerical power.
When explaining shape, link the full chain: greater curvature causes stronger refraction, giving a shorter focal length and therefore a greater magnitude of lens power.
A diverging lens has a negative focal length and negative power under the usual sign convention.
Create a free account to read GCSE Physics revision notes for your exam board and track your progress.