Explanation:
Cut off wavelength is given by
$\lambda_{\text{min}}=\frac{\text{hc}}{\text{eV}'}$
where h = Planck's constan
c = speed of light
e = charge on an electron
V = potential difference applied to the tube
When potential difference (V) applied to the tube is doubled, cutoff wavelength
$\big({\lambda}'_\text{min}\big)$ is given by
${\lambda}'_\text{min}=\frac{\text{hc}}{\text{e}(2\text{V})}$
$\Rightarrow\lambda'_\text{min}=\frac{\lambda_\text{min}}{2}$
Cuttoff wavelength does not depend on the separation between the filament and the target.
Thus, cutoff wavelength will be halved if the the potential difference applied to the tube is doubled.
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To an observer on the earth the stars appear to twinkle. This can be ascribed to
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(a) The fact that stars do not emit light continuously |
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(b) Frequent absorption of star light by their own atmosphere |
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(c) Frequent absorption of star light by the earth's atmosphere |
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(d) The refractive index fluctuations in the earth's atmosphere |
Assertion : Microwave communication is preferred over optical communication.
Reason : Microwaves provide large number of channels and band width compared to optical signals.
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(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
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(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
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(c) If assertion is true but reason is false. |
|
(d) If the assertion and reason both are false. |
Assertion : The temperature coefficient of resistance is positive for metals and negative for P-type semiconductor.
Reason : The effective charge carriers in metals are negatively charged whereas in P-type semiconductor they are positively charged.
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(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
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(d) If the assertion and reason both are false. |
$\alpha<\beta$
$\alpha<\beta \text{ if}\text{ A}<\text{B}$
$\alpha<\beta \text{ if}\text{ A}>\text{B}$
$\alpha<\beta \text{ if}\text{ A}=\text{B}$
When there is an electric current through a conducting wire along its length, then an electric field must exist
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(a) Outside the wire but normal to it |
(b) Outside the wire but parallel to it |
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(c) Inside the wire but parallel to it |
(d) Inside the wire but normal to it |
A battery of 6 volts is connected to the terminals of a three metre long wire of uniform thickness and resistance of the order of 100 Ω. The difference of potential between two points separated by 50 cm on the wire will be
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(a) 1 V |
(b) 1.5 V |
(c) 2 V |
(d) 3 V |
In the experiment of diffraction at a single slit, if the slit width is decreased, the width of the central maximum
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(a) Increases in both Fresnel and Fraunhofer diffraction |
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(b) Decreases both in Fresnal and Fraunhofer diffraction |
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(c) Increases in Fresnel diffraction but decreases in Fraunhofer diffraction |
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(d) Decreases in Fresnel diffraction but increases is Fraunofer diffraction. |