Given,
$\int_\text{s}\text{E.dS}=0$
It means the algebraic sum of number of flux lines entering the surface and number of flux lines leaving the surface.
Now, from Gauss' law,
$\int_\text{S}\text{E.dS}=\frac{\text{q}}{\in_0}$
Where q is charge enclosed by the surface.
Now,
$\int_\text{s}\text{E.dS}=0$
q = 0 i.e., net charge enclosed by the surface must be zero.
Hence, all other charges must necessarily be outside the surface.
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Assertion : The ferromagnetic substance do not obey Curie’s law.
Reason : At Curie point a ferromagnetic substance start behaving as a paramagnetic substance.
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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. |
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(d) If the assertion and reason both are false. |
A concave mirror of focal length 15 cm forms an image having twice the linear dimensions of the object. The position of the object when the image is virtual will be
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(a) 22.5 cm |
(b) 7.5 cm |
(c) 30 cm |
(d) 45 cm |
A wire of length 100 cm is connected to a cell of emf 2 V and negligible internal resistance. The resistance of the wire is 3 W. The additional resistance required to produce a potential drop of 1 milli volt per cm is
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(a) 60 W |
(b) 47 W |
(c) 57 W |
(d) 35 W |
A uniform wire of 16 Ω is made into the form of a square. Two opposite corners of the square are connected by a wire of resistance 16 Ω. The effective resistance between the other two opposite corners is
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(a) 32 Ω |
(b) 20 Ω |
(c) 8 Ω |
(d) 4 Ω |
An electric line of force in the xy plane is given by equation 
. A particle with unit positive charge, initially at rest at the point x = 1, y = 0 in the xy plane
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(a) Not move at all |
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(b) Will move along straight line |
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(c) Will move along the circular line of force |
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(d) Information is insufficient to draw any conclusion |
The mass of a neutron is the same as that of
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(a) A proton |
(b) A meson |
(c) An epsilon |
(d) An electron |
In a double slit arrangement fringes are produced using light of wavelength 4800 Å. One slit is covered by a thin plate of glass of refractive index 1.4 and the other with another glass plate of same thickness but of refractive index 1.7. By doing so the central bright shifts to original fifth bright fringe from centre. Thickness of glass plate is
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(a) 8 mm |
(b) 6 mm |
(c) 4 mm |
(d) 10 mm |