1) Do > 2f
Do means object distance
2f means 2 x focal length
2 x focal length = radius of curvature
When an object is placed beyond the radius of curvature, a real image is formed between the radius of curvature and focus. The image size is reduced. The sketch is shown below
Answer:
Explanation:
The formula for hydrogen atomic spectrum is as follows
energy of photon due to transition from higher orbit n₂ to n₁

For layman series n₁ = 1 and n₂ = 2 , 3 , 4 , ... etc
energy of first line

10.2 eV
wavelength of photon = 12375 / 10.2 = 1213.2 A
energy of 2 nd line

= 12.08 eV
wavelength of photon = 12375 / 12.08 = 1024.4 A
energy of third line

12.75 e V
wavelength of photon = 12375 / 12.75 = 970.6 A
energy of fourth line

= 13.056 eV
wavelength of photon = 12375 / 13.05 = 948.3 A
energy of fifth line

13.22 eV
wavelength of photon = 12375 / 13.22 = 936.1 A
I'm not sure but I know u is 10^6
Should be an air tight seal