In which of the following, emission of electrons does not take place
- thermionic emission
- X-rays emission
- photoelectric emission
- secondary emission
The Correct Option is B
Solution and Explanation
Secondary emission : When an electron strikes the surface of a metallic plate, it emits other electrons from the surface.
Photoelectric emission : Emission o felectrons from the metal surface on irradiation with radiation of suitable frequency
X-rays emission : They are due to transitions in the inner energy levels of the atom
Top Questions on Electromagnetic waves
- A plane electromagnetic wave of frequency 20 MHz travels in free space along the +x direction. At a particular point in space and time, the electric field vector of the wave is \( E_y = 9.3 \, \text{V/m} \). Then, the magnetic field vector of the wave at that point is:
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- Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Electromagnetic waves carry energy but not momentum.
Reason (R): Mass of a photon is zero. In the light of the above statements, choose the most appropriate answer from the options given below:- JEE Main - 2025
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- A plane electromagnetic wave propagates along the \( +x \) direction in free space. The components of the electric field \( \vec{E} \) and magnetic field \( \vec{B} \) vectors associated with the wave in Cartesian frame are:
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- The magnetic field of an E.M. wave is given by: \[ \vec{B} = \left( \frac{\sqrt{3}}{2} \hat{i} + \frac{1}{2} \hat{j} \right) 30 \sin \left( \omega \left( t - \frac{z}{c} \right) \right) \] The corresponding electric field in S.I. units is:
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- Match Electromagnetic waves listed in Column I with Production method/device in Column II.
The correctly matched combination is as in option :- CUET (UG) - 2024
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Questions Asked in NEET exam
- Given below are two statements :
Statement I : In the nephron, the descending limb of loop of Henle is impermeable to water and permeable to electrolytes.
Statement II : The proximal convoluted tubule is lined by simple columnar brush border epithelium and increases the surface area for reabsorption.
In the light of the above statements, choose the correct answer from the option given below :- NEET (UG) - 2024
- Nephrons
Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A : The potential (V) at any axial point, at 2 m distance(r) from the centre of the dipole of dipole moment vector\(\vec{P}\) of magnitude, 4 × 10-6 C m, is ± 9 × 103 V.
(Take \(\frac{1}{4\pi\epsilon_0}=9\times10^9\) SI units)
Reason R : \(V=±\frac{2P}{4\pi \epsilon_0r^2}\), where r is the distance of any axial point, situated at 2 m from the centre of the dipole.
In the light of the above statements, choose the correct answer from the options given below :- NEET (UG) - 2024
- Magnetic Field
- \(^{290}_{82}X\stackrel{\alpha}{\rightarrow}Y\stackrel{e^+}{\rightarrow}Z\stackrel{\beta^-}{\rightarrow}P\stackrel{e^-}{\rightarrow}Q\)
In the nuclear emission stated above, the mass number and atomic number of the product Q respectively, are :- NEET (UG) - 2024
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- In an ecosystem if the Net Primary Productivity (NPP) of first trophic level is 100x (kcal m-2)yr-1, what would be the GPP (Gross Primary Productivity) of the third trophic level of the same ecosystem?
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The output (Y) of the given logic gate is similar to the output of an/a :
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Concepts Used:
Electromagnetic waves
The waves that are produced when an electric field comes into contact with a magnetic field are known as Electromagnetic Waves or EM waves. The constitution of an oscillating magnetic field and electric fields gives rise to electromagnetic waves.
Types of Electromagnetic Waves:
Electromagnetic waves can be grouped according to the direction of disturbance in them and according to the range of their frequency. Recall that a wave transfers energy from one point to another point in space. That means there are two things going on: the disturbance that defines a wave, and the propagation of wave. In this context the waves are grouped into the following two categories:
- Longitudinal waves: A wave is called a longitudinal wave when the disturbances in the wave are parallel to the direction of propagation of the wave. For example, sound waves are longitudinal waves because the change of pressure occurs parallel to the direction of wave propagation.
- Transverse waves: A wave is called a transverse wave when the disturbances in the wave are perpendicular (at right angles) to the direction of propagation of the wave.