{"id":18510,"date":"2015-12-02T15:19:24","date_gmt":"2015-12-02T09:49:24","guid":{"rendered":"https:\/\/www.cbselabs.com\/?p=18510"},"modified":"2021-09-18T15:27:18","modified_gmt":"2021-09-18T09:57:18","slug":"important-questions-for-class-12-physics-cbse-ac-currents","status":"publish","type":"post","link":"https:\/\/www.cbselabs.com\/important-questions-for-class-12-physics-cbse-ac-currents\/","title":{"rendered":"Important Questions for CBSE Class 12 Physics AC Currents"},"content":{"rendered":"

Alternating Current\u00a0Important Questions for CBSE Class 12 Physics AC Currents<\/strong><\/span><\/h2>\n

1<\/strong>.Phasor<\/strong> The representation of AC current and voltage by rotating vectors is calle^ phasor and the diagram representing these phasors is known as phasor diagram. The length of the vector represents the maximum or peak value. The projection of the vectors on fixed axis gives the instantaneous value of alternating current and voltage.<\/p>\n

2.In an AC Circuit Containing Resistance Only<\/strong><\/p>\n

Suppose a resistor of resistance R is connected to an AC source of emf with instantaneous value E is given by<\/p>\n

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\n3.In an AC Circuit Containing Capacitor Only<\/strong><\/p>\n

Suppose a capacitor with capacitance C is connected to an AC source with emf having instantaneous value E is given by<\/p>\n

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\n4. In an AC Circuit Containing Inductor Only<\/strong><\/p>\n

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\n10 .L-C Oscillations<\/strong>
\nConsider the L-C circuit shown as below:<\/strong><\/p>\n

\"important-questions-for-class-12-physics-cbse-ac-currents-10\"<\/p>\n

When the charged capacitor is connected with the inductor, current flows through the inductor and energy stored in the inductor in the form of magnetic field and capacitor discharges and vice-versa. In this way, energy oscillates between capacitor and inductor. If the circuit is not ideal oscillations finally die away.
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\n\"important-questions-for-class-12-physics-cbse-ac-currents-11\"<\/p>\n

Previous Years Examination Questions<\/strong><\/span><\/h3>\n

1 Mark Questions<\/strong><\/span><\/h3>\n

1.A reactive element in an AC circuit causes the current flowing<\/strong>
\n\"important-questions-for-class-12-physics-cbse-ac-currents-1q\"<\/p>\n

Ans<\/strong>
\n\"important-questions-for-class-12-physics-cbse-ac-currents-1\"<\/p>\n

2 Marks Questions\u00a0<\/strong><\/span><\/h3>\n

2.A capacitor C, a variable resistor R and a bulb B are connected in series to the AC mains in the circuit as shown. The bulb glows with some brightness. How will the glow of the bulb change if (i) a dielectric slab is introduced between the plates of the capacitor keeping resistance R to be the same (ii) the resistance R is increased keeping the same capacitance? [Delhi 2014]<\/strong>
\n\"important-questions-for-class-12-physics-cbse-ac-currents-2q\"<\/p>\n

Ans.<\/strong>
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\n\"important-questions-for-class-12-physics-cbse-ac-currents-3q\"<\/p>\n

Ans.<\/strong>
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\nAns<\/strong>.Refer to ans3
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\nAns<\/strong> Refer to ans3.
\n\"important-questions-for-class-12-physics-cbse-ac-currents-6q\"<\/p>\n

Ans.<\/strong>
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\n7. In a series L-C-R circuit, obtain the\u00a0conditions under which (i) the impedance of circuit is minimum and (ii) wattless current flows in the circuit.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 [Foreign 2014]<\/strong><\/p>\n

Ans.<\/strong>
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\n\"important-questions-for-class-12-physics-cbse-ac-currents-7a\"<\/p>\n

\"important-questions-for-class-12-physics-cbse-ac-currents-8q\"<\/p>\n

Ans.<\/strong>
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Ans.<\/strong>
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Ans.<\/strong><\/p>\n

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\n\"important-questions-for-class-12-physics-cbse-ac-currents-11q\"<\/p>\n

Ans.<\/strong>
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Ans.<\/strong>
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\n13.(i) The graphs (I) and (II) represent the\u00a0variation of the opposition offered by the circuit element to the flow of alternating current with frequency of the applied emf. Identify the circuit element corresponding to each graph.<\/strong>
\n(ii) Write the expression for the impedance offered by the series combination of the above two elements connected across the AC sources. Which will be ahead in phase in this circuit, voltage or current?<\/strong>
\n\"important-questions-for-class-12-physics-cbse-ac-currents-13q\"<\/p>\n

Ans.<\/strong>
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\n14. An AC source of voltage V = Vm<\/sub> sin wt is applied across a series L-C-R Draw the phasor diagram for this circuit when the<\/strong><\/p>\n