Question

A camera lens has a power of +1.75D. If the diameter of the lens is 5.7 cm, what is the f-stop of the lens?

Does a single-lens camera produce a real or virtual image? Explain?

A farsighted person has a near point of 38 cm. She holds her book at 25 cm to read, what is the focal length and power of the lens necessary for her to read?

An electron travels at a velocity of 7.5x10^6 m/s through a 0.333 T magnetic field. What is the radius of the electron path?

Ag-112 goes through ?-decay then ?^- decay, what are the intermediary and final daughter products?

An unknown isotope goes through ?-decay then ?^- decay and results in Po-210. What are the initial and intermediary parents?

What are the ranges of temperatures of a glowing object that will result in light within the visual spectrum?

Answer 1

#1we know,

so f for the given question is, 1/1.75 m=0.571 m=57.1 cm

f-stop=57.1/5.7=f10

#2 a camera by definition is an optical instrument that captures and records images. now for capturing an image of an object on any artificial screen, it is necessary that the light rays coming from the object meet at a point on or near the screen, and a real image be formed. if a virtual image is fomed by the camera lense it cannot be obtained on the film.

#3 in case of far sightedness the near point of the eye lens shifts away from the eye. in the given question, the near point of the eye has shifted from 25cm to 38cm. so we have to use a corrective lens which make the object situated ata distance of 25 cm from the eye appear at a distance of 38 cm.

u=-25cm , v=-38cm f=? we have to use the lens formula for findig the focal length of the required lens:

this leads to f=+73.07cm=+0.73m ( convex lens), power of the lens=1/f=1/0.73m=1.36D

#4 when an elctron enters a magnitic field such that the velocity is perpedicular to the field it experiences a centripetal force which makes it travel in a circular path. the force experienced by an elctron in a field is ,

where v is velocity of elctron, B is the field and e is charge of the elctron. this force is equal to centripetal force