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Assertion and Reason Type Questions : Assertion : Metals like Na or K, emit electrons even when visible lights fall on them . Reason : This is because their work function is low.
Photoelectric emission occurs only when the incident light has more than a certain minimum
Photoelectric emission occurs only when the incident light has more than a certain minimum frequency. This is because only photons with energy greater than the work function of the material can cause the emission of electrons. The energy of a photon is given by the formula $E = hf$, where $h$ is Planck's constant and $f$ is the frequency. Thus, a minimum frequency is required to provide sufficient energy to overcome the work function and release electrons.
Theshold-Frequency is equal to = …………………….$\times 10^ {14} Hz $
$ \phi _0 = hf $ $ \therefore f_0 = { \phi_0 \over h} ={ 3.3 \times 1.6 \times 10^{-19} \over 6.6 \times 10^{-34} }$ $ \therefore f_0 = 0.8 \times 10^{15} $ $ \therefore f_0 = 8.0 \times 10^{14} Hz $
An electron is accelerated under a potential difference of 64 V, the de Broglie wave length associated with electron is .......... ... $A ^ \circ $ (Use charge of electon = 1.6 \times 10^{-19} ,C = 9.1 \times 10^{-31} Kg , mass of electron h = 6.623\times 10 ^ {-34} J.sec ) $
$ \lambda = { 12.27 \over \sqrt v } $ $ = { 12.27 \over \sqrt {64} } = { 12.27 \over 8} =1.553 $ $ \therefore \lambda = 1.534 A ^\circ $
A $\alpha $ particle and proton has same K.E. The ratio of de Broglie wavelength of a $ \alpha $ particle and proton is....
$ K = { p^2 \over 2m } $ $ \therefore p = \sqrt {2Km} $ $ \lambda = h/p = h / \sqrt{2Km} $ $ \therefore \lambda \alpha { 1 \over \sqrt m } $ $ \therefore { \lambda_\alpha \over \lambda_p } = \sqrt{m_p \over m_x} = \sqrt { 1/4} $ $ \therefore { \lambda_\alpha \over \lambda_p } = { 1 \over 2 } $
If $\alpha $ - particle and proton have same velocities, the ratio of de Broglie wavelength of $ \alpha $ -particle and proton is ....
If $ \alpha $ - particle and proton are accelerated through the same potential difference, then the ratio of de Brogile wavelength of $ \alpha $- particle and proton is ........
$ K = vq $ $ { 1 \over 2 } mv^2 = Vq , m^2 v^2 = 2Vqm $ $ \therefore mv = \sqrt { 2Vqm} $ $ \lambda = { h \over mv } = { h \over \sqrt { 2Vqm } } $ $ \therefore \lambda \alpha { 1 \over \sqrt { qm } }$ $ \therefore { \lambda_\alpha \over \lambda_p} = \sqrt { q_p m_p \over q_\alpha m_\alpha } = \sqrt { em_p \over 2e \times 4m_p } = \sqrt { 1 \over 8} $ $ \therefore {\lambda_\alpha \over \lambda_p } = { 1 \over 2 \sqrt 2 } $
Read the paragraph carefully and select the proper choice from given multiple choices. According to Einstein whena photon of light of frequeny f or wavelength $ \lambda $ is incident on a photo sensitive metal surface of work function $ \phi $ . Where $ \phi < hf $ (here h is Plank's constant) then the emission of photo-electronss place takes place. The maximum K.E. of emitted photo electrons is given by $K_max = hf-\phi $. If the therehold frequency of metal is $ f_0$ then $ hf_0 = \phi $ . (ii) Stopping potential of emitted photo-electron is =........... V.
Matching type questions : (Match, Column-I and Column-II property)
Column-I
(A) Planck's theory of quanta
(B) Einstein's theory of quanta.
(C) Bohr's stationary orbit
(D) D-Broglie waves
Column-II
(p) Light energy= hv
(q) Angular momentumofelectron in anorbit
(r) Oscillator energies
(s) Electron microscope
Let's match the concepts from Column I with their corresponding properties in Column II:
(A) Planck's theory of quanta: This theory relates to the quantization of oscillator energies, where energy is given by discrete packets called quanta (r).
(B) Einstein's theory of quanta: This theory is related to the photoelectric effect, where light energy is given by hv, indicating that light consists of packets of energy called photons (p).
(C) Bohr's stationary orbit: Bohr's model postulates that electrons revolve in specific orbits with quantized angular momentum (q).
(D) D-Broglie waves: D-Broglie hypothesized that particles like electrons exhibit wave-like properties, which is crucial in the functioning of devices like electron microscopes (s).
So the correct matching is: (A-r) (B-p) (C-q) (D-s).
Matching type questions : (Match, Column-I and Column-II property) Column-I (A) Particle nature of light (B) Wave nature of light (C) Wave nature of slow moving electrons (D) Wave nature of fast moving electrons Column-II (p) Davisson and Germer (q) G. P. Thomson (r) Max. Planck (s) Muygen
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