1
WB JEE 2019
MCQ (Single Correct Answer)
+1
-0.25
Change Language
When the frequency of the light used is changed from $$4 \times {10^{14}}{s^{ - 1}}$$ to $$5 \times {10^{14}}{s^{ - 1}}$$, the angular width of the principal (central) maximum in a single slit Fraunhoffer diffraction pattern changes by 0.6 radian. What is the width of the slit (assume that the experiment is performed in vacuum)?
A
$$1.5 \times {10^{ - 7}}$$ m
B
$$3 \times {10^{ - 7}}$$ m
C
$$5 \times {10^{ - 7}}$$ m
D
$$6 \times {10^{ - 7}}$$ m
2
WB JEE 2019
MCQ (Single Correct Answer)
+2
-0.5
Change Language
A capacitor of capacitance C is connected in series with a resistance R and DC source of emf E through a key. The capacitor starts charging when the key is closed. By the time the capacitor has been fully charged, what amount of energy is dissipated in the resistance R?

WB JEE 2019 Physics - Current Electricity Question 25 English
A
$${1 \over 2}C{E^2}$$
B
0
C
CE2
D
$${{{E^2}} \over R}$$
3
WB JEE 2019
MCQ (Single Correct Answer)
+2
-0.5
Change Language
A horizontal fire hose with a nozzle of cross-sectional area $${5 \over {\sqrt {21} }} \times {10^{ - 3}}{m^2}$$ delivers a cubic metre of water in 10s. What will be the maximum possible increase in the temperature of water while it hits a rigid wall (neglecting the effect of gravity)?
A
$$1^\circ $$C
B
$$0.1^\circ $$C
C
$$10^\circ $$C
D
$$0.01^\circ $$C
4
WB JEE 2019
MCQ (Single Correct Answer)
+2
-0.5
Change Language
Two identical blocks of ice move in opposite directions with equal speed and collide with each other. What will be the minimum speed required to make both the blocks melt completely, if the initial temperatures of the blocks were $$-$$8$$^\circ$$C each? (Specific heat of ice is 2100 Jkg$$-$$1K$$-$$1 and latent heat of fusion of ice is 3.36 $$ \times $$ 105 Jkg$$-$$1)
A
840 ms$$-$$1
B
420 ms$$-$$1
C
8.4 ms$$-$$1
D
84ms$$-$$1
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