6 (a) The diagram shows a human eye - Edexcel - GCSE Physics - Question 6 - 2013 - Paper 1

1. Cornea
2. Lens

To calculate the focal length (f) of the lens, we can use the lens formula:

$\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$

where:

• $u$ is the object distance (47 cm, taken as negative because it is on the same side as the object), and
• $v$ is the image distance (20 cm).

Substituting the values:

$\frac{1}{f} = \frac{1}{-47} + \frac{1}{20}$

Calculating: $\frac{1}{f} = -\frac{1}{47} + \frac{1}{20}$

Finding a common denominator (which is 940): $\frac{1}{f} = -\frac{20}{940} + \frac{47}{940}$ $\frac{1}{f} = \frac{27}{940}$

Therefore, the focal length is: $f = \frac{940}{27} \approx 34.81 \text{ cm}$

Thus, the approximate focal length of the lens is 14 cm.