What is the equivalent capacitance (in μF) for the circuit given below?

In the given circuit the capacitance C1 and C2 are parallel with the capacitance C3 i.e
(C1 || C2) + C3
∴(20 × 30) ⁄ (20 + 30) + 20
CA= 12 + 20 = 32 μF
Now capacitance CA, C4, & C5 are in the series therefore
Ceqv = (1/30 + 1/20 + 1/20)
Ceqv = (60/8) = 7.5 μF
 

 Which of the following statement is CORRECT?

Although the Thevenin’s theorem and Norton’s theorem can be used to solve a given network, yet the circuit approach differs in the following respects:
A Norton’s theorem is converse (opposite) of Thevenin’s theorem in the respect that Norton equivalent circuit uses a current generator instead of the voltage generator and the resistance RN (which is the same as RTH) in parallel with the generator instead of being in series with it.
Thevenin’s theorem is a voltage form of an equivalent circuit whereas Norton’s theorem is a current form of an equivalent circuit.
To Convert Thevenin equivalent circuit into Norton’s equivalent circuit the following step is involved
RN = RTH
IN = ETH ⁄ RTH
 

What is the value of Norton resistance (in Ω) between the terminal A and B for the given Norton’s equivalent circuit?

Norton equivalent resistance for the given network is
R = (R1 || R2) + R3
R = (4 || 8) + 2 = (4 x 8) ⁄ (4 + 8) + 2 = 5.6Ω
Norton equivalent resistance = 5.6Ω

 What will be the resistance (in ohms) of a lamp rated at 220 V, 200 W?

The power can be defined as
P = V2 ⁄ R
Given
P = 200 W
V = 220 V
200 = 2202 ⁄ R
R = 242 Ω
 

Which property of an electrical conductor opposes a change in the current?

An inductor is a device which temporarily stores energy in the form of the magnetic field. It is usually a coil of wire. One of the basic property of the electromagnetism is that when you have current flowing through the wire it creates a small magnetic field around it.
One current first start to flow through the inductor a magnetic field start to expand then after some time magnetic field becomes constant then we have some energy stored in the magnetic field.
Once a constant magnetic field is generated in the Inductor, it will not change any further. As magnetic flux = N x I (Turns x Current), Inductor will draw a constant current to maintain the magnetic field.
Once current stop flowing the magnetic field start to collapse and the magnetic energy turned back into electric energy.
So when the current flowing through an inductor changes, the magnetic field also changes in the inductor and emf (electromotive force) is induced in the inductor as per Faraday’s law of electromagnetic induction.
According to Lenz’s law, the direction of electromotive force(emf) opposes the change of current that created it.  V= -Lx dI/dt (rate of change of current)
So inductor opposes any change of current through them.

 Two wires of the same resistivity have equal length. The cross-sectional area of first wire is two times to the area of the other. What will be the resistance (in ohms) of the wire that has a large cross-sectional area, if the resistance of the other wire is 20 Ohms?