For getting a sharp image, we have to use light of suitable wavelength. This is because focal length of a lens depends upon wavelength.

Two sources of light having same frequency and zero or constant, intial phase difference are called coherent sources.

The focal length of the lens in water \({ f }_{ w }=\cfrac { { n }_{ g }-1 }{ \frac { { n }_{ g } }{ { n }_{ w } } -1 } \) 
As \({ n }_{ g }>{ n }_{ w },\cfrac { { n }_{ g } }{ { n }_{ w } } >1\) ,so f_w > f_a
That is focal length of lens in water will increase, but the nature of lens will remain unchanged.

The distance between the pole and the focus is called the focal length (f) of the mirror.

\(\lambda =\frac { h }{ \sqrt { 2mqV } } ;\lambda '=\frac { h }{ \sqrt { 2me(4V) } } =\frac { \lambda }{ 2 } \)

No, most electrons get scattered into the metal. Only a few come out of the surface of the metal.

Its working depends on the electron emission from a metal cathode due to irradiation of light or other radiations.

Household robots are used as vacuum cleaners, floor cleaners, gutter cleaners, lawn mowing, pool cleaning, and to open and close doors.

Manipulation of colours by adjusting the size of nano particles with which the materials are made.

The undesired electrical signals are termed as noise. When a signal is transmitted, the undesired signals get mixed with it, leading to distortion of the signal.

The range of frequencies required to transmit a piece of specified information in a particular channel is called channel bandwidth or the bandwidth of the transmission system.

Digital electronics deals with logical operations. The variables are called logical variables

A graph is plotted by taking the forward bias voltage (V) along the x- axis and the current (I) through the diode along y-axis. This graph is called the forward V-I characteristics.

\(_{ 86 }^{ 220 }{ Rn }\rightarrow _{ 84 }^{ 216 }{ Po }+_{ 2 }^{ 4 }{ He }\)
The mass number of Po = 216
The atomic number of Po = 84
The mass number of He=  4
The atomic number of He = 2

(i) A nuclear chain reaction dies out, when the neutrons produced so fast they escape from the uranium without interacting.
(ii) When the neutrons are lost due to the. extremely small size of uranium (i.e, smaller than critical size).

(i) Speed of Electromagnetic wave \(=\frac{Peak\ value\ of\ Electric\ field}{Peak\ value\ of\ magnetic\ field}\)
\(c=\frac { { E }_{ 0 } }{ { B }_{ 0 } } \)
(ii) Yes, As Electromagnetic waves contain both electric and magnetic fields, there is a non-zero energy density associated with it.
\(E=\frac { hc }{ \lambda } \)
Momentum p \(=\frac{Total\ energy\ transferred\ to\ the\ surface}{Velocity\ of\ light\ in\ vacuum}\)
i.e.p = \(\frac{U}{c}=mc\)
U - total energy transferred to the surface.
EM waves carry not only energy and momentum but also angular momentum.

Yes, If the dielectric constant of the medium is increased, there will be a decrease of potential.

This is due to the fact that
(i) electric field is radial
(ii) electric field E ∝ \(\frac{1}{R^2}\)

(i) Angle of dip (90°) is maximum at the magnetic piles.
(ii) Vertical component of earth's magnetic field is zero at magnetic equator.

The angle subtended by the Earth's total magnetic field \(\vec { B } \) with the horizontal direction in the magnetic meridian is called dip or magnetic inclination (I) at that point.

The current in the coil will flow clockwise the direction of current will be from P to Q in coil PQ and from C to D in coil CD.

At the transmitting point, the voltage is increased and the corresponding current is decreased by using a step-up transformer. Then it is transmitted through transmission lines. This reduced current at high voltage reaches the destination without any appreciable loss. At the receiving point, the voltage is decreased and the current is increased to appropriate values by using a step-down transformer, and then it is given to consumers.

The resistors value of carbon resistors changes considerably during storage and use.

The resistance by the electrolytic of a cell to the flow of circuit between its electrodes is called internal resistance.

(i) When d battery is disconnected, the capacitance increase from C₀ to C
(ii) New potential difference between the plates
\(V=\frac { { Q }_{ 0 } }{ C } =\frac { { C }_{ 0 }{ V }_{ 0 } }{ C } =\frac { { C }_{ 0 }{ V }_{ 0 } }{ { \varepsilon }_{ r }{ C }_{ 0 } } =\frac { { V }_{ 0 } }{ { \varepsilon }_{ r } } \)

Energy density U\(=\frac { 1 }{ 2 } { \varepsilon }_{ 0 }{ E }_{ 2 }\)
But \(E=\frac { \sigma }{ { \varepsilon }_{ 0 } } =\frac { Q }{ { A\varepsilon }_{ 0 } } \)
\(\therefore U=\frac { 1 }{ 2 } .\frac { { \varepsilon }_{ 0 }{ Q }_{ 2 } }{ { A }^{ 2 }{ \varepsilon }_{ 0 } } \Rightarrow U=\frac { { Q }_{ 2 } }{ 2A^{ 2 } } \)
\(U\alpha \frac { 1 }{ { A }^{ 2 } } \Rightarrow { U }_{ A }>{ U }_{ B }\)

(i) The dipole moment of dipole \(|\overset { \rightarrow }{ P } |=q\times 2a\)
Force on -q at A = -q \(\overset { \rightarrow }{ E } \)
Force on + q at B = +q\(\overset { \rightarrow }{ E } \)
Net force on the dipole = q\(\overset { \rightarrow }{ E } \)- q\(\overset { \rightarrow }{ E } \) = 0
(ii) Work done on dipole when it is rotated through 180°
W = ∆U = pE (cos θ₁ - cos θ₂)
= pE (cos 0° - cos180^o)
= pE(1 - (-1)
W = 2pE

When an external electric field is applied, the dipoles inside the polar molecule tend to align in the direction of the electric field. Hence a net dipole moment is induced in it. Then the dielectric is said to be polarized by an external electric field.