Without corrective lenses, a near-siqhtrd person can see clearly only objects th

Question

Without corrective lenses, a near-siqhtrd person can see clearly only objects that are within 100 cm from his eyes. The person has normal vlston lenses. What type of lens are the contact lenses, and what is their focal length diverging, -100 cm converging, 100 cm diverging, -50 cm converging, 50 cm diverging, -200 cm A person can see dearly, objects that are between 1 meter and any larger distance from their eyes. What is required to restore their vision to normal' a diverging lens of focal length -20 cm a diverging lens of focal length -33.3 cm a converging lens of focal length 33.3 cm a converging lens of focal length 20 cm a converging lens of focal length -20 cm In a Young s douWe-siit expenment. the distance from the central maximum on the screen to the first minimum is 2.0 mm. The slits are separated by d = 200a, where A is the wavelength of the incident light. What is the distance from slits to screen? a. 0.200 m b. 0.800 m c. 0.267 m d. 0.400 m e. 8.00 m

Explanation / Answer

Number 1)

We will take objects from infinity and form images at 100 cm, so

1/f = 1/p + 1/q

1/f = 1/infinity + 1/-100

f = -100

The the lenses are diverging with a focal length of -100 cm (Choice A)

Number 2)

We need to take objects at a norma near point of 25 cm and form the images at 1 m (100 cm)

1/f = 1/p + 1/q

1/f = 1/25 + 1/-100

f = 33.3 cm

Thus we need a convergin lens with a focal length of 33.3 cm (Choice C)

Number 3)

Apply y/L = m(wavelength)/d

(.002)/L = 1/200

L = .4 m - Choice D

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