The ratio of the magnitudes of the electric fields at the surfaces of the two spheres is
- A$\frac{r_1}{r_2}$
- B$\frac{r_2}{r_1}$
- C$\frac{r_2^2}{r_1^2}$
- D$\frac{r_1^2}{r_2^2}$
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How should people wearing spectacles work with a microscope?
The following diagram indicates the energy levels of a certain atom when the system moves from 2E level to E, a photon of wavelength λ is emitted. The wavelength of photon produced during its transition from
level to E is

|
(a) λ/3 |
(b) 3 λ/4 |
(c) 4 λ/3 |
(d) 3 λ |
Missing lines in a continuous spectrum reveal
|
(a) Defects of the observing instrument |
|
(b) Absence of some elements in the light source |
|
(c) Presence in the light source of hot vapours of some elements |
|
(d) Presence of cool vapours of some elements around the light source |
A radioactive element emits 200 particles per second. After three hours 25 particles per second are emitted. The half life period of element will be
|
(a) 50 minutes |
(b) 60 minutes |
(c) 70 minutes |
(d) 80 minutes |