An isolated 16 μF parallel plate air capacitor has a potential differences of 1000 V (Figure 5 a). A dielectric slab having relative permittivity (i.e. dielectric constant) = 5 is introduced to fill the space between the two plates com pletely. (Figure 5 b). Calculate:
(i) The new capacitance of the capacitor.
(ii) The new potential differences between the two plates of the capacitor
An electron revolves around the nucleus of hydrogen atom in a circular orbit of radius 5 x 10-11 m. Calculate
(i) Intensity of electric field of the nucleus at the position of the electron.
(ii) Electrostatic potential energy of the hydrogen nucleus and electron system.
In the circuit shown below, PQ is a uniform metallic wire of length 4 m and resistance 20 Ω. Battery B has an emf of 10V and internal resistance of 1 Ω. J is a jockey or slide contact. Resistance of the ammeter and connecting wires is negligible.
(i) When the jockey J does not touch the wire PQ, what is the reading of ammeter A?
(ii) Where should the jockey J be pressed on the wire PQ so that the galvanometer G shows no deflection?
(i) What is the effect of each of the magnetic fields on the needle?
(ii) When the needle is in equilibrium, obtain an expression for an angle θ made by the needle with in terms
of only.
(i)
The needle is under the action of two perpendicular and uniform magnetic field BF and Bh.
This will set a couple of force on the needle as BF out in a direction opposite to BH.
This will tend to rotate the needle.
(ii)
When the needle is in equilibrium position then will make an angle θ with the direction of BH.
Let the pole strength of the N and S be the m.
Then moment of couple due to field BF = m x BH x SA
Moment of couple due to field BH = m x BF x NA
In the equilibrium position the moments of two couples are equal.
M x BH x SA = m x BF x NA
SA / NA x BH = BF
BH = BF
BF = BH tan θ
Hence proved.