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Questions Related to physics

Multiple choice physics alternating current power in ac circuits average power in ac circuit and power factor power in ac circuit

A resistance $R\Omega$ is connected in series with capacitance $C$ Farad value of impedance of the circuit is $10\Omega$ and $R=6\Omega$ so, find the power factor of circuit.

  1. $0.4$

  2. $0.6$

  3. $0.67$

  4. $0.9$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In an RC circuit, the impedance Z = sqrt(R^2 + Xc^2). Given Z = 10 and R = 6, then 100 = 36 + Xc^2, so Xc = 8. The power factor is cos(phi) = R/Z = 6/10 = 0.6.

Multiple choice physics alternating current power in ac circuits average power in ac circuit and power factor power in ac circuit

In an AC circuit $V$ and $I$ are given by $V=100\sin{\left(100t\right)}$volt, $I=100\sin{\left(100t+\dfrac{\pi}{3}\right)}$amp the power dissipated in the circuit is

  1. $5.0\ kW$

  2. $2.5\ kW$

  3. $1.25\ kW$

  4. $zero$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
$P={V} _{rms}\times{I} _{rms}\times\cos{\phi}$
$=\dfrac{{V} _{\circ}{I} _{\circ}}{2}\cos{\phi}$
$=\dfrac{100\times 100}{2}\times \dfrac{1}{2}$
$=2500$W
$=2.5$kW
Multiple choice physics alternating current power in ac circuits average power in ac circuit and power factor power in ac circuit

The current and voltage functions in an AC circuit are$i = 100\sin 100tmA$ , $V = 100\sin \left( {100t + \cfrac{\pi }{3}} \right)V$ The power dissipated in the circuit is

  1. 10 W

  2. 2.5 W

  3. 5 W

  4. 5 kW
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$i=100sin 100tmA$
$v=100 sin(100t+\frac {x}{3})V$
$P=I _{rms}\times V _{rms} cos\theta$
$=\frac {100}{\sqrt 2}\times \frac {100}{\sqrt 2}\times \frac {1}{2}\times 10^{-3}W$
$=\frac {10}{4}=2\cdot 5W$

Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

In an open pipe, the pressure variation at the ends of the pipe is maximum.

  1. True

  2. False

  3. Nither

  4. Either
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A suction at the end of the tube draws air from further up the tube, and that in turn draws air from further up the tube and so on. So the result is that a pulse of high pressure air travelling down the tube is reflected as a pulse of low pressure air traveling up the tube. So the pressure wave has been reflected at the open end, with a change in phase of 180. In the open-open pipe, there is such a reflection at both ends. So the above argument is false.

Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

Two understand oscillators are known to have the same neutral frequency $ \omega _0 $ . The mass and damping coefficient of the first oscillator are $m _1 $ and $b _1 $ , and the mass and damping coefficient of the second oscillator are $m _2 $ and $b _2$ , respectively. A sinusoidal driving force of $F _{ext} = F _0 \cos \omega t $ is applied to each oscillator. Starting with $\omega $ far from $ \omega _0$ the driving force is tuned in order to observe resonant behavior. If $ m _1 = 4 m _2 $ and $b _1 = 2b _2 $ , then which one the following statements concerning the driven oscillations is correct?

  1. The resonant peak of the first driven oscillator is higher and narrower than that of the second oscillator.

  2. The resonant peak of the first driven oscillator is higher and wider than that of the second oscillator.

  3. The resonant peak of the first driven oscillator is lower and wider than that of the second oscillator.

  4. The resonant peak of the first driven oscillator is lower and narrower than that of the second oscillator.
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

A student is performing the experiment of resonance Column. The diameter of the column tube is $4\ cm$. The frequency of the tuning fork is $512\ Hz$. The air temperature $38^{o}C$ in which the speed sound is $336\ m/s$. The zero of the meter scale coincides with the top end of the Resonance Column tube. When the first resonance occurs, the reading of the water level in the column is:

  1. $14.0\ cm$

  2. $15.2\ cm$

  3. $16.4\ cm$

  4. $17.6\ cm$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For $I^{st}$ resonance

$l _1 + e = \dfrac{\lambda}{4}$ or $l _1 = \dfrac{\nu}{4f} - 0.3d = 15.2\space cm$

Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

If two vibrating systems are in resonance, then :

  1. Their amplitudes are equal

  2. Their frequencies are equal

  3. Their temperatures are equal

  4. Their intensities are equal
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Answer is C.

Resonance is a phenomenon that consists of a given system being driven by another vibrating system or by external forces to oscillate with greater amplitude at some preferential frequencies. Frequencies at which the response amplitude is a relative maximum are known as the system's resonant frequencies, or resonance frequencies. 
When both the bodies vibrate, they will start to vibrate with the same frequency.

Multiple choice physics free, damped and forced oscillations resonance: examples and uses resonance oscillatory motion

State whether the given statement is True or False :
One example of resonance involving visible and invisible light in the electromagnetic spectrum is resonance fluorescence. 

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

One example of resonance involving visible and invisible light in the electromagnetic spectrum is resonance fluorescence. Fluorescence itself is a process whereby a material absorbs electromagnetic radiation from one source, then re-emits that radiation on a wavelength longer than that of the illuminating radiation. 

Among its many applications are the fluorescent lights found in many homes and public buildings. Sometimes the emitted radiation has the same wavelength as the absorbed radiation, and this is called resonance fluorescence.
Resonance fluorescence is used in laboratories for analyzing phenomena such as the flow of gases in a wind tunnel.