Question

a)A simple microscope using a single lens often shows coloured image of a white source. Why? b)A magnifying glass is a converging lens placed close to the eye. A farsighted person uses spectacles having converging lenses. Compare the functions of a converging lens used as a magnifying glass and as spectacles.

Answer 1

a)  A simple microscope uses single convex lens.

• sometimes due to spherical aberrations and chromatic, the image of a white source seems coloured at the corners of the lens and somewhere in between.

b)  A converging lens in a magnifying glass consists of smaller focal length which is used to magnify an object which is placed close to the lens[In between P and F ]

• Whereas converging lens used in  spectacles is of varying focal length which depends upon the actual near point of the hypermetropia.

It forms image at the near point of the defected eye which is further focussed by the eye lens.

Answer 2

ᴀ)  ᴀ sɪᴍᴘʟᴇ ᴍɪᴄʀᴏsᴄᴏᴘᴇ ᴜsᴇs sɪɴɢʟᴇ ᴄᴏɴᴠᴇx ʟᴇɴs.

sᴏᴍᴇᴛɪᴍᴇs ᴅᴜᴇ ᴛᴏ sᴘʜᴇʀɪᴄᴀʟ ᴀʙᴇʀʀᴀᴛɪᴏɴs ᴀɴᴅ ᴄʜʀᴏᴍᴀᴛɪᴄ, ᴛʜᴇ ɪᴍᴀɢᴇ ᴏғ ᴀ ᴡʜɪᴛᴇ sᴏᴜʀᴄᴇ sᴇᴇᴍs ᴄᴏʟᴏᴜʀᴇᴅ ᴀᴛ ᴛʜᴇ ᴄᴏʀɴᴇʀs ᴏғ ᴛʜᴇ ʟᴇɴs ᴀɴᴅ sᴏᴍᴇᴡʜᴇʀᴇ ɪɴ ʙᴇᴛᴡᴇᴇɴ.
ʙ)  ᴀ ᴄᴏɴᴠᴇʀɢɪɴɢ ʟᴇɴs ɪɴ ᴀ ᴍᴀɢɴɪғʏɪɴɢ ɢʟᴀss ᴄᴏɴsɪsᴛs ᴏғ sᴍᴀʟʟᴇʀ ғᴏᴄᴀʟ ʟᴇɴɢᴛʜ ᴡʜɪᴄʜ ɪs ᴜsᴇᴅ ᴛᴏ ᴍᴀɢɴɪғʏ ᴀɴ ᴏʙᴊᴇᴄᴛ ᴡʜɪᴄʜ ɪs ᴘʟᴀᴄᴇᴅ ᴄʟᴏsᴇ ᴛᴏ ᴛʜᴇ ʟᴇɴs[ɪɴ ʙᴇᴛᴡᴇᴇɴ ᴘ ᴀɴᴅ ғ ]

ᴡʜᴇʀᴇᴀs ᴄᴏɴᴠᴇʀɢɪɴɢ ʟᴇɴs ᴜsᴇᴅ ɪɴ  sᴘᴇᴄᴛᴀᴄʟᴇs ɪs ᴏғ ᴠᴀʀʏɪɴɢ ғᴏᴄᴀʟ ʟᴇɴɢᴛʜ ᴡʜɪᴄʜ ᴅᴇᴘᴇɴᴅs ᴜᴘᴏɴ ᴛʜᴇ ᴀᴄᴛᴜᴀʟ ɴᴇᴀʀ ᴘᴏɪɴᴛ ᴏғ ᴛʜᴇ ʜʏᴘᴇʀᴍᴇᴛʀᴏᴘɪᴀ.
ɪᴛ ғᴏʀᴍs ɪᴍᴀɢᴇ ᴀᴛ ᴛʜᴇ ɴᴇᴀʀ ᴘᴏɪɴᴛ ᴏғ ᴛʜᴇ ᴅᴇғᴇᴄᴛᴇᴅ ᴇʏᴇ ᴡʜɪᴄʜ ɪs ғᴜʀᴛʜᴇʀ ғᴏᴄᴜssᴇᴅ ʙʏ ᴛʜᴇ ᴇʏᴇ ʟᴇɴs.