A fixed amplitude V0 and AC voltage source of variable angular frequency are joined in series with capacitance C and an electric bulb of resistance R (inductance zero). When variable angular frequency is increased:

As per the given values, When Variable Angular Frequency ω is increased, the following can occur:

The amplitudes of the voltages, in an AC circuit, across the components and the current are treated as vectors. Simply, the phase difference between voltage and current is apparently the angle between the vectors.

Now, assume the amplitude of the flowing current in the circuit = i

Therefore, magnitude of voltage vector of given resistance, V= iR … [1]

\(\therefore\) Because voltage across resistance and current always are in phase, thereby the vectors of the voltage of resistance (VR) and current (i) are found to be parallel.

Capacitance, in an AC circuit, serves as resistance to the circuit’s flow, also called the reactance of the circuit (Xc).

Thus,

Value of capacitive reactance equals, X= 1/ωC … [2]

Here,

  • ω = Angular Frequency of the Source
  • C = Capacitance

Therefore, magnitude of the given voltage vector of capacitance equals, V= iX… [3]

A phase difference of −π/2 between the capacitor voltage and the current is found. The capacitor voltage lags the current behind by a phase of π/2. Thus, the vector of capacitor voltage (Vc) is found at an angle of −π/2 from the current vector.

Therefore, the resultant or the net voltage in the circuit is equal to, Vnet = V+ VC.

Note: “VR and VC are vectors and hence, Vnet is also a vector.”

Therefore, the magnitude of net voltage equals, Vnet = √V2R + V2

Now, after value substitution of VR and VC from equations [1] and [3].

⇒ Vnet = √(iR)+ (iXC)2

⇒ Vnet=i√R+ 1/ω2C2

Here, Vnet = V0

I = V0/√R+ 1ω2C2

Considering the value of ω is increased, the value of the current [1] will also increase. Now, the dissipated power via the resistance is expressed as P = i2R. Thus, the power in the given circuit will also rise. Now, if the power of the bulbs increases, it is more likely to glow brighter.

Check More: Class 12 Physics Notes


Related Questions

  1. In A Graph Between Current I And Voltage V, Find The Portion Corresponding To Negative Resistance.
  2. A Closed Coil Has 500 Turns Across Rectangular Frame Of Area 4.0 Cm2 With Resistance Of 500 Ohms. The Coil Is Plane Perpendicular To A Uniform Magnetic Field Of 0.2wb/M2. Find Amount Of Charge Through Coil If Turned Over (180 Degrees Rotation).
  3. 1.0 M Rectangular Loop With A Sliding Connector Is In Uniform Magnetic Field 2t Perpendicular To Plane Of Loop. Resistance Is 2 Ohms. Two Resistances, 6 Ohms And 3 Ohms, Are Connected.
  4. Resistance In Meter Bridge’s Two Arms Are 5 Ohms And R Ohms. When Resistance R Is Shunted With Equal Resistance, New Balance Point Becomes 1.6l1. Calculate R.
  5. If R, C And L Are Fundamental Quantities In A Circuit Like Resistance, Capacitance And Inductance In W, Then Find Dimensional Formula For Resistance And Capacitance.
  6. Two Copper Wires, Of 1 M And 9 M Respectively, Have Same Resistance. Find Their Diameters In Ratio.
  7. Two Identical Resistors With Resistances 15 Ohm Are Connected In Series And Parallel To A Battery Of 6 V. Calculate Ratio Of Power Consumed.
  8. Two Concentric Coplanar Circular Loops Of Wire (Resistance Per Unit Length 10 4 Ohms M-1) Have Diameters 0.2 M And 2 M. With Time-Varying Potential Difference Of (4+2.5t) Applied To Larger Loop, Find Current In Smaller One.
  9. Three Incandescent Bulbs (Each 100 W) Are Attached In Series. In Another Circuit, Three More Bulbs Of Same Wattage Are Attached Parallelly To An Equal Source.
  10. A Circuit Consists Of A Battery Of 3 Cells (2 V Each), A Combination Of Three Resistors, 10 Ohm, 20 Ohm And 30 Ohm, Attached Parallelly, With Plug Key And Ammeter (In Series).
  11. For The Resistor Combination, Find The Equivalent Resistance Between M and N.

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CBSE CLASS XII Related Questions

  • 1.
    The figure shows three point charges kept at the vertices of triangle ABC. The net electric field, due to this system of charges, at the midpoint M of base BC will be:

      • \( \frac{q}{4 \pi \epsilon_0 l^2} \) pointing along MA
      • \( \frac{q}{\pi \epsilon_0 l^2} \) pointing along AM
      • \( \frac{q}{2 \pi \epsilon_0 l^2} \) pointing along AM
      • Zero

    • 2.
      Assertion (A) : The mass of a nucleus is less than the sum of the masses of the constituent nucleons. Reason (R) : Energy is absorbed when the nucleons are bound together to form a nucleus.

        • Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
        • Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
        • Assertion (A) is true, but Reason (R) is false.
        • Both Assertion (A) and Reason (R) are false.

      • 3.
        If both the number of protons and the neutrons are conserved in each nuclear reaction, in what way is mass converted into energy (or vice versa) in a nuclear reaction? Explain.


          • 4.
            Draw a circuit diagram of a full-wave rectifier using p-n junction diodes. Explain its working and show the input-output waveforms.


              • 5.
                A square loop of side 0.50 m is placed in a uniform magnetic field of 0.4 T perpendicular to the plane of the loop. The loop is rotated through an angle of 60° in 0.2 s. The value of emf induced in the loop will be:

                  • 5 V
                  • 3.5 V
                  • 2.5 V
                  • Zero V

                • 6.
                  If Bohr’s quantization postulate (angular momentum \( = \frac{nh}{2\pi} \)) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why, then, do we never speak of quantization of orbits of planets around the Sun? Explain.

                    CBSE CLASS XII Previous Year Papers

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