Question

The radii of curvatures of two convex lenses 0.5m and o.5m.its refractive index is 1.5. what is its focal lengths​

Answer 1

ᴘᴏᴡᴇʀ ᴏꜰ ᴄᴏᴍʙɪɴᴀᴛɪᴏɴ ᴘ=1.5 ᴅɪᴏᴘᴛʀᴇ

ᴘᴏᴡᴇʀ ᴏꜰ ᴄᴏɴᴠᴇx ʟᴇɴꜱ ʜᴀᴠɪɴɢ ꜰᴏᴄᴀʟ ʟᴇɴɢᴛʜ ᴏꜰ 0.5ᴍ, ᴘ

1

=

0.5

1

ᴅɪᴏᴘᴛʀᴇ

ᴜꜱɪɴɢ ᴘ=ᴘ

1

+ᴘ

2

∴ 1.5=

0.5

1

+ᴘ

2

ᴡᴇ ɢᴇᴛ ᴘ

2

=−0.5 ᴅɪᴏᴘᴛʀᴇ

ᴛʜᴜꜱ ꜰᴏᴄᴀʟ ʟᴇɴɢᴛʜ ᴏꜰ ꜱᴇᴄᴏɴᴅ ʟᴇɴꜱ ꜰ

2

=

ᴘ

2

1

⟹ ꜰ

2

=−

0.5

1

=−2ᴍ (ɴᴇɢᴀᴛɪᴠᴇ ꜱɪɢɴ ɪᴍᴘʟɪᴇꜱ ᴛʜᴇ ʟᴇɴꜱ ᴍᴜꜱᴛ ʙᴇ ᴀ ᴄᴏɴᴄᴀᴠᴇ ʟᴇɴꜱ)

ᴛʜᴜꜱ ꜱᴇᴄᴏɴᴅ ʟᴇɴꜱ ᴄᴏᴜʟᴅ ʙᴇ ᴄᴏɴᴄᴀᴠᴇ ʟᴇɴꜱ ᴏꜰ ꜰᴏᴄᴀʟ ʟᴇɴɢᴛʜ 2ᴍ.