# MHCET 2012

$\alpha$ rays are doubly charged He
i.e. Helium nuclei which are not electromagnetic waves. Others belong to electromagnetic spectrum having different wavelengths.
1
#458903
Solution
Which of the following is not an electromagnetic wave?
A
Light rays
B
X-rays
C
Alpha rays
D
Gamma rays
The range  100 $A^0$ to 400$A^0$ come under visible spectrum.
2
#458906
Solution
Electromagnetic waves of wavelength ranging from  $100\overset {\circ}{A}$ to $400 \overset {\circ}{A}$ comes under
A
X-rahs
B
UV region
C
Visible region
D
Infrared region
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.
3
#458908
Solution
Electromagnetic theory suggests that the light consists of:
A
Magnetic vector only
B
Electric vector only
C
Electric and magnetic vectors perpendicular to each other
D
Parallel electric and magnetic vector
Wavelength, $\lambda = 10 \: m$

Using the relation $\nu=\dfrac{c}{ \lambda }= \dfrac{ 3 \times 10^8}{10}= 3 \times 10^7\: Hz$
4
#458909
Solution
The frequency of radio waves corresponding to a wavelength of $10\ m$ is
A
$3\times 10^{7} Hz$
B
$3.3\times 10^{8} Hz$
C
$3\times 10^{9} Hz$
D
$3\times 10^{-7} Hz$
Electromagnetic waves travel in free space or vacuum with the velocity of light, $c= 3 \times 10^8\:m/s$.
5
#458910
Solution
The electromagnetic waves travel in free space with the velocity of
A
Sound
B
Light
C
Greater than that of light
D
Greater than that of sound
The existence of electromagnetic waves were experimentally confirmed by German Scientist Hertz.
6
#458911
Solution
The existence of electromagnetic waves were experimentally confirmed by
A
Maxwell
B
C
Hertz
D
Tesla
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.
7
#458912
Solution
The back emf in a DC motor is maximum when
A
the motor has picked up maximum speed.
B
the motor has just started moving.
C
the speed of motor is still on increase.
D
the motor has just been switched off.
AC measuring instrument (AC ammeter and voltmeter) always measures rms value.
8
#458913
Solution
AC measuring instrument measures
A
peak value
B
rms value
C
any value
D
average value
The quality factor (Q-factor) of a resonant circuit
$Q = \dfrac {\omega_{0}L}{R}$
At resonance, $\omega_{0} = \dfrac {1}{\sqrt {LC}}$
$\therefore Q = \dfrac {1}{\sqrt {LC}} \cdot \dfrac {L}{R} = \dfrac {1}{R} \sqrt {\dfrac {L}{C}}$
9
#458914
Solution
The Q-factor of a resonant circuit is equal to
A
$\dfrac {1}{L}\sqrt {\dfrac {R}{C}}$
B
$\dfrac {1}{R} \sqrt {\dfrac {L}{C}}$
C
$\dfrac {1}{RL} \sqrt {C}$
D
$\dfrac {1}{C}\sqrt {\dfrac {R}{L}}$
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 $V_p \gt V_s$, $n_p \gt n_s$
10
#458915
Solution