i.e. Helium nuclei which are not electromagnetic waves. Others belong to electromagnetic spectrum having different wavelengths.

The range 100 $$A^0$$ to 400$$A^0$$ come under visible spectrum.

Electromagnetic theory suggests that light is a vibration of electric field and magnetic field vectors mutually perpendicular to each other and both being perpendicular to the direction of propagation of electromagnetic wave.

Wavelength, $$\lambda = 10 \: m$$

Using the relation $$\nu=\dfrac{c}{ \lambda }= \dfrac{ 3 \times 10^8}{10}= 3 \times 10^7\: Hz$$

Electromagnetic waves travel in free space or vacuum with the velocity of light, $$c= 3 \times 10^8\:m/s$$.

The existence of electromagnetic waves were experimentally confirmed by German Scientist Hertz.

The value of back emf is proportional to the motor speed. So, back emf is maximum when the motor has picked up the maximum speed.

AC measuring instrument (AC ammeter and voltmeter) always measures rms value.

The quality factor (Q-factor) of a resonant circuit $$Q = \dfrac {\omega_{0}L}{R}$$ At resonance, $$\omega_{0} = \dfrac {1}{\sqrt {LC}}$$ $$\therefore Q = \dfrac {1}{\sqrt {LC}} \cdot \dfrac {L}{R} = \dfrac {1}{R} \sqrt {\dfrac {L}{C}}$$

In a step-down transformer, the number of turns of the primary coil are more than the number of turns of the secondary. If $$V_p$$ and $$V_s$$ are primary and secondary voltages and $$n_p$$ and $$n_s$$ are no of turns in primary and secondary coils $$\dfrac{V_p}{V_s} = \dfrac{n_p}{n_s}$$ In a step down transformer, output voltage is less than input voltage. Since $$V_p \gt V_s$$, $$n_p \gt n_s$$