Practice free Alternating Current (Physics) NEET multiple-choice questions online with instant answers and detailed explanations. No login required.
A resistor and a capacitor are connected in series with an ac source. If the potential drop across the capacitor is 5 V and that across resistor is 12 V, the applied voltage is,
with help pf phasor $ \upsilon = \sqrt {\upsilon _R^2 + \upsilon _C^2 } $
In an ac circuit the emf (e) and the current (i) at anyinstant core given respectively by $ e = E_0 sin \Omega t , I =I_0 sin ( \Omega t - \varphi ) $. The average power in the circuit over one cycle of ac is.
The average power in an AC circuit is given by the formula: \[ P_{avg} = \frac{E_0 I_0}{2} \cos \varphi \] where \( E_0 \) is the peak emf, \( I_0 \) is the peak current, and \( \varphi \) is the phase difference between the emf and the current. This formula is derived from the general power formula for AC circuits and accounts for the phase difference.
An alternating current of frequency 'f' is flowing in a circuit containing a resistance R and a choke L in series. The impedance of this circuit is
The impedance \( Z \) of a series circuit containing resistance \( R \) and inductance \( L \) is given by: \[ Z = \sqrt{R^2 + (\omega L)^2} \] where \( \omega = 2\pi f \) is the angular frequency. Substituting \( \omega \), the impedance becomes: \[ Z = \sqrt{R^2 + (2\pi fL)^2} \]
The resistance of an R-L circuit is $ 10 \Omega $ . An emf $E_O$ applied across the circuit at $ \omega = 20 rad/s $. If the $ { I_0 \over \sqrt 2 } $ current in the ckt is 2 what is the value of L
$ I = { \epsilon _0 \over \sqrt { R^2 + \omega^2 L^2 } } = { \epsilon _0 \over R \sqrt {1 + ({ \omega L \over R }) ^2 }} = { I _0 \over \sqrt {1 + ({ \omega L \over R }) ^2 }}$
A resistor $ 30 \Omega $ , inductor of reactance $ 10 \Omega $ and the capacitor of reactance $ 10 \Omega $ are connected in series to an ac voltage source$ e = 300 \sqrt 2 sin (\omega t) $ The current in the circuit is
$ I_{rms } = { \upsilon _ {rms } \over |z| } =300 /30 = 10 A $
Same current is flowing in two alternating circuits.The first circuits contains only inductance andthe other contains only a capacitor. If the frequency of the emf of ac is increased the effect on the value of the current will be.
In an inductive circuit, the current \( I \) is inversely proportional to the frequency \( f \) of the AC supply, according to the formula \( I = \frac{V}{\omega L} \). Thus, as frequency increases, the current decreases. In a capacitive circuit, the current is directly proportional to the frequency, according to \( I = \omega CV \). Hence, as frequency increases, the current increases. Therefore, the effect of increasing frequency is a decrease in current for an inductive circuit and an increase in current for a capacitive circuit.
A 20 volts ac is applied to a circuit consisting of a resistance and a coil with negligible resistance. If the voltage across the resistance is 12 V, the voltage across the coil is,
An alternating voltage $ E=200 \sqrt 2 sin (100t) $ is connected to 1 microfarad capacitor through an ac ammeter. The reading of the ammeter shall be.
An LCR series circuit with $ R = 100 \Omega $ is connected to a 200 V, 50 Hz a.c source when only the capacitance is removed the current lies the voltage by $ 60 ^ \circ $ when only the inductance is removed, the current leads the voltage by $ 60 ^\circ $ . The current in the circuit is
for inductor $ tan \theta = { \omega L \over R } $ for capacitor $ tan \theta = { 1 \over \omega CR } $ $ |\theta | is same 50 , \omega L = { 1 \over \omega C } $ means resonance $I _ {rms} = { \upsilon _{rms} \over R} $
The power factor of a good choke coil is
The power factor of a choke coil depends on the phase difference between the voltage and the current. For a good choke coil, which is highly inductive, the phase difference is close to 90 degrees. The power factor (
$$ cos \\phi $$
) is given by:
$$ cos \\phi = \\cos (90^\circ) $$
$$ cos \\phi = 0 $$
However, in practical scenarios, it is not exactly zero due to the presence of some resistance. Therefore, it is nearly zero. Thus, the power factor of a good choke coil is nearly zero.
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