Two concentric conducting thin spherical shells A and B having radii rA and rB ( rB > rA ) are charged to QA and - QB (). The electrical field along a line, (passing through the centre is)
Dimension of electrical resistance is
[ M L2 T-3 A-1 ]
[ M L2 T-3 A-2 ]
[ M L3 T-3 A-2 ]
[ M L-1 T3 A2 ]
Four point + ve charges of same magnitude (Q) are placed at four corners of a rigid square frame as shown in figure. The plane of the frame is perpendicular to Z-axis. If a -ve point charge is placed at a distance z away from the above frame ( z < < l ) then
-ve charge oscillates along the Z-axis
it moves away from the frame
it moves slowly towards the frame and stays in the plane of the frame
it moves slowly towards the frame and stays in the plane of the frame
Assertion: A body that is a good radiator is also a good absorber of radiation at a given wavelength.
Reason: According to Kirchoff's law the absorptivity of a body is equal to its emissivity at a given wavelength
If both assertion and reason are true and reason is the correct explanation of assertion
If both assertion and reason are true but reason is not the correct explanation of assertion
If assertion is true but reason is false
If both assertion and reason are false
For skywave propagation of a 10 MHz signal, what should be the minimum electron density in ionosphere?
∼ 1.2 × 1012 m-3
∼ 106 m-3
∼ 1014 m-3
∼ 1022 m-3
What should be the maximum acceptance angle at the air-core interface of an optical fibre if n1 and n2 are the refractive indices of the core and the cladding, respectively?
sin-1( n2/n1 )
sin-1
B.
sin-1
'i' is max acceptance angle (incidence angle ) air core interface which make 'r' as refraction angle ( 90° r ) as critical angle at core cladding interface making refraction angle 90°
angle 1 is i, angle 2 is r, angle 3 is r , angle is 4 is (90° r ), angle 5 is 90°
At air core interface
By snell's law
n sin i = nsin r
For air n = 1
sin i = n1 sin r
at core cladding interface
n1 sin (90° r ) = n2 sin 90°
n1 cosr =
sin i =
=
sini = n1 sinr
=
Acceptance angle = arc sin
So total internal reflection angle has to be less than Acceptance angle.
Consider an n-p-n transistor amplifier in the common emitter configuration. The current gain of the transistor is 100. If the collector current changes by 1 mA, what will be the change in emitter current?
1.1 mA
1.01 mA
0.01 mA
10 mA
A telescope has an objective lens of focal length 200 cm and an eye piece with focal length 2 cm. If this telescope is used to see a 50 meter tall building at a distance of 2 km, what is the height of the image of the building formed by the objective lens?
5 cm
10 cm
1 cm
2 cm
The ground state energy of hydrogen atom is -13.6 eV. What is the potential energy of the electron in the state?
0 eV
-27.2 eV
1 eV
2 eV