Radiations of intensity 0.5 W/m² are striking a metal plate.The pressure on the plate is

0.166 × 10^–8N/m²
0.332 × 10^–8N/m²
0.111 × 10^–8N/m²
0.083 × 10^–8N/m²

Solution

Two insulating plates are both uniformly charged in such a way that the potential difference between them is V₂ – V₁= 20 V. (i.e., plate 2 is at a higher potential). The plates are separated by d = 0.1 m and can be treated as infinitely large. An electron is released from rest on the inner surface of plate 1. What is its speed when it hits plate 2?(e = 1.6 × 10^–19C,m_e= 9.11 × 10^–31kg)

2.65 × 10⁶m/s
7.02 × 10¹²m/s
1.87 × 10⁶m/s
32 × 10^–19 m/s

Solution

In a photoelectric effect experiment, for radiation with frequency v₀ with hv₀= 8eV, electrons are emitted with energy 2 eV.What is the energy of the electrons emitted for incoming radiation of frequency 1.25 v₀?

1 eV
3.25 eV
4 eV
9.25 eV

Solution

Which one of the following graphs represents the variation of maximum kinetic energy (EK) of the emitted electrons with frequency v inphotoelectric effect correctly ?

Solution

hv – hv₀= E_k, according to photoelectric equation,

when v = v₀, E_k = 0.

Graph (d) represents E_k – v relationship.

If 5% of the energy supplied to a bulb is radiated as visible light, the number of visible quanta emitted per second by a 100 W bulb, assuming the wavelength of visible light to be 5.6 × 10^–5cm,is

1.4 × 10¹⁹
1.4 × 10²⁰
2 × 10¹⁹
2 × 10²⁰

Solution

A small photocell is placed at a distance of 4 m from a photosensitive surface. When light falls on the surface the current is 5 mA. If the distance of cell is decreased to 1m,the current will become

1.25 mA
(⁵⁄₁₆)5 mA
20 mA
80 mA

Solution

\(I\alpha \frac{1}{d^{2}}\)

The momentum of photon whose frequency f is

\(\frac{hf}{c}\)
\(\frac{hc}{f}\)
\(\frac{h}{f}\)
\(\frac{c}{hf}\)

Solution

In a photo-emissive cell with exciting wavelength λ, the fastest electron has speed V. If the exciting wavelength is changed to 3λ/4, the speed of the fastest emitted electron will be :