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.
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Which of the following is not an electromagnetic wave?
A
Light rays
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B
X-rays
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C
Alpha rays
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D
Gamma rays
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The range  100 $$A^0$$ to 400$$A^0$$ come under visible spectrum.
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Electromagnetic waves of wavelength ranging from  $$100\overset {\circ}{A}$$ to $$400 \overset {\circ}{A}$$ comes under
A
X-rahs
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B
UV region
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C
Visible region
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D
Infrared region
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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.
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Electromagnetic theory suggests that the light consists of:
A
Magnetic vector only
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B
Electric vector only
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C
Electric and magnetic vectors perpendicular to each other
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D
Parallel electric and magnetic vector
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Wavelength, $$\lambda = 10 \: m$$

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