The electric field associated with an electromagnetic wave in vaccum is given by E = i 40 cos (kz − 6 x 108 t), where E, Z and t are in volt m-1, metre and second respectively. The value of wave vector (k) is
2 m-1
0.5 m-1
6 m-1
3 m-1
In the shown figure, what is the potential difference between the points A and B and between B and C respectively in steady state ?
VAB = VBC = 100 V
VAB = 75 V , VBC = 25 V
VAB = 25 V , VBC = 75 V
VAB = VBC = 50 V
A resistance of 4 Ω and a wire of length 5 m and resistance 5 Ω are joined in series and connected to a cell of emf 10 V and internal resistance of 1 Ω. A parallel combination of two identical cells in balanced across 3 m of the wire. The emf E of each cell is
1.5 V
3.0 V
0.67 V
1.33 V
An L-C-R series circuit with 100 Ω resistance is connected to an AC source of 200 V and angular frequency 300 rad s-1 . When only the capacitance is removed, the current lags behind the voltage by 60°. When only the inductance is removed, the current leads the voltage by 60°. The average power dissipated in this L-C-R circuit is
0
400 W
200 W
800 W
Two concentric conducting spherical shells A and B having radii rA and rB (rB > rA) are charged to QA and -QB . The electric field along a line passing through the centre is
Electrons with de-Broglie wavelength λ fall on the target in an X-ray tube. The cut-off wavelength of the emitted X-rays is
The figure illustrates how the flux density B inside a sample of demagnetised ferromagnetic material varies with the magnetic flux density B0 , in which the sample is kept. For the sample to be suitable for making a permanent magnet, then which statement is true for this?
OQ should be large, OR should be small
both OQ and OR should be large
OQ should be small and OR should be large
both OQ and OR should be small
B.
both OQ and OR should be large
For the permanent magnet, the material should has high retentivity (so that the magnet is strong and high coercivity (so that the magnetising is not wiped out by stray magnetic fields), Hence, option (b) is true for given situation.
Two straight infinitely long current carrying wires are kept along Z-axis at the co-ordinates (0, a, O) and (0, -a, 0) respectively, as shown in figure. The current in each of the wire is equal and along negative Z-axis (into the plane of the paper).
The variation of magnetic field on the X-axis will be approximately
The co-ordinates of centre of mass of the uniform lamina shown in figure, is if smal disc of radius is cut from disc of radius a
A toroid having 200 turns carries a current of 1A. The average radius of the toroid is 10 cm. The magnetic field at any point in the open space inside the toroid is
4 × 10-3 T
0.5 × 10-3 T
0
3 × 10-3 T