# Year 10 GCSE Paper question varies inversely as the square

• July 10th 2008, 03:50 AM
rob12341
Year 10 GCSE Paper question varies inversely as the square
The shutter speed, S, of a camera varies inversely as the square of the aperture setting, f.

When f= 8, S= 125

a) find a formula for S in terms of f.

b) Hence, or otherwise calculate the value of S when f= 4

thanks for any time anybody spends on this question

Rob
• July 10th 2008, 03:57 AM
Chop Suey
If x varies inversely to y, then:
$x = \frac{k}{y}$
Where k is the constant value for any values of (x,y).

If x varies inversely to the square of y, then:

$x = \frac{k}{y^2}$

Find the constant, and then replace in the equation:
$S = \frac{k}{f^2}$

Use this equation to find (b).