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
A.
-ve charge oscillates along the Z-axis
The negative charge oscillates, the resultant force acts as a restoring force and is cosθ component, proportional to displacement. When it reaches the plane XY, the resultant force is zero and the mass moves down due to inertia. Thus oscillation is set.
This problem is similar to below diagram
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
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