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| Physics 12th Chapter 16 - Alternating Current |
Physics 12th Chapter 16 - Alternating Current Solved MCQs, Important Short Questions and Long Questions Bank
MCQs
Please select the right answer.
1. 100µF capacitor is connected to an alternating voltage of 24V and frequency 50Hz. The reactance of the capacitor is
2. A capacitor is a perfect insulator for:
3. A capacitor is perfect insulator for
4. A changing electric flux creates a
5. A changing magnetic field creates
6. A choke is preferred to a capacitor to decrease the A.C in a circuit because the capacitor:
7. A device that allows only the continuous flow of AC through a circuit is:
8. A device which opposes the flow of A.C only is
9. A pure inductive coil is that which has:
10. A sinusoidal current has rms value of 10A. its maximum value is
11. A device which allows only the continuous flow of an A.C., through a circuit is:
12. A.C can be measure with the help of:
13. A.C varies as function of:
14. A.C voltmeter measures:
15. AC source used in Pakistan is:
16. Alternating current can be measured by D.C ammeter because if:
17. Alternating current can be produced by:
18. Alternating current is converted to direct current by:
19. Alternating current is one which changes in a:
20. Alternating current is produced by a voltage source which polarity:
21. Alternating current or emf measuring instruments measures its:
22. Alternating voltage is:
23. An A.C Voltmeter reads 220V, its peak value will be
24. An A.C. varies as a function of
25. An inductor may store energy in its:
26. As a result of modulation, the resultant wave is known as:
27. As series resonance in L.C.R circuit, the impedance is equal to:
28. At high frequency RLC series circuit shows the behavior of
29. At high frequency the value of reactance of capacitor will be
30. At high frequency, the current through a capacitor is:
31. At resonance frequency in an R.L.C series circuit, VL and Vc:
32. At resonance frequency the current in RLC series circuit is
33. At resonance frequency the impedance of RLC parallel circuit is
34. At resonance frequency, the impedance of an R.L.C series circuit is:
35. At resonance RLC series circuit shows the behavior of
36. At resonance the value of current in RLC series circuit is
37. At what frequency I henry inductance offer same impendance as IF capacitor:
38. At what frequency will an inductor of 0 H have a reactance of 500?
39. Average value of current and voltage over a complete cycle is
40. Capacitor will have a large reactance at
41. Choke consumes extremely small:
42. Component of circuit which controls current
43. current is opposed by
44. Direct current cannot flow through
45. During each cycle AC voltage reaches a peak value
46. Electrical resonance in an LCR A.C circuit is very sharp if:
47. Electromagnetic waves consist of
48. Electromagnetic waves do not transport
49. Electromagnetic waves transmitted form an antenna are
50. Electromagnetic weaves transport
51. Energy in an inductance coil is stored in the form of:
52. For modulation purpose, high frequency radio waves are called:
53. For parallel resonant circuit, the resonance current is:
54. For q – t graph, slope shows:
55. If frequency f is in Hz and capacitance C is in F then the unit of Xc is:
56. If frequency fis in Hz and inductance L is in milli henry, then XL is in:
57. If I₀ is the peak value of A.C. current, its root mean square value
58. If I₀is the peak value of A.C. current, then average value of current
59. If the capacitive reactance of AC circuit is made four times then the frequency of the circuit becomes:
60. If the frequency of AC supplied is doubled then the capacitor reactance becomes
61. If the peak value of A.C. voltage is 10√2 , then its root mean square value will be
62. If V₀is the peak value of A.C. voltage, its root mean square value
63. If Vᵣₘₛ=10√2 then peak voltage V₀ is
64. Impedance is composed of
65. Impedance is the combined effect of:
66. In a purely capacitive A.C circuit, the current is:
67. In a resistive A.C circuit, instantaneous values of voltage and current are:
68. In a three phase A.C. supply the phase difference in voltage of any two phases
69. In A.C circuits, current and voltage is controlled by:
70. In A.C circuits, the A.C instruments indicate:
71. In an A.C. circuit with resistor only, the current and voltage have a phase angle of
72. In an A.C. circuit with capacitor only the current
73. In an electromagnetic wave, the electric and magnetic fields are
74. In an RLC circuit, the impedance is:
75. In capacitor
76. In case of capacitor, S.I. unit of reactance is
77. In comparison to D.C transmission losses in A.C are:
78. In electromagnetic waves, the electric and magnetic fields are:
79. In free space the speed of electromagnetic waves is
80. In frequency modulation, the amplitude of carrier waves is:
81. In L.C parallel circuit, the coil draws:
82. In modulation, low frequency signal is known as:
83. In Pakistan, the frequency of A.C supply is
84. In pure capacitor Ac circuit, the current I and q are
85. In pure resistive A.C circuit, instantaneous voltage or current
86. In RLC series circuit the condition for resonance is
87. In three phase A.C supply coils are inclined at an angle of
88. In three phase voltage across any two five lines is about
89. In tuning circuit if capacitance is doubled and inductance is halved then its frequency
90. In which of the following, the loss of energy is less:
91. Inductive reactance (DL of a coil is expressed in:
92. Main reason for worldwide use of A.C is:
93. Maxwell’s equations were discovered by James Clark Maxwell in
94. Metal detector consist of
95. Modulation is achieved by changing the:
96. Modulation is the process of:
97. 100 F capacitor is connects to an AC-voltage of 24 V and frequency 50Hz. The reactance of the capacitor is
98. Ohm is the unit of
99. One complete set of positive and negative value of alternating quantities is called:
100. Phase difference between V and I of an A C through resistor is:
101. Power dissipated in pure conductor is:
102. Power dissipation in a pure inductive or in a pure capacitance circuit is:
103. Power factor is defined by:
104. Power factor is equal to:
105. Pure choke consumes:
106. Radio frequency choke is:
107. Resistance of choke is:
108. Resonance frequency fr =
109. Resonance frequency of parallel resonance circuit is fr =
110. Resonance frequency of series resonance circuit is fr =
111. S.I. unit of impedance is
112. The alternating current can be transmitted:
113. The alternating voltage or current is actually measured by:
114. The amplitude modulation A.M transmission frequencies range from:
115. The amplitude of the effective current is:
116. The average value of alternating voltage over a complete cycle is:
117. The basic circuit element in a D.C circuit is:
118. The basic circuit elements in A.C circuits are:
119. The capacitive reactance to pure DC is
120. The circuit in which current and voltage are in phase, the power factor is:
121. The combined effect of resistance and reactance in a circuit is
122. The condition of resonance in an R.L.C series circuit is that:
123. The current which changes its direction through the circuit for a complete cycle is called
124. The current which keeps on reversing its direction with time is
125. The direction of propagation of an electromagnetic waves is
126. The effective value of any sinusoidal alternating current or voltage is defined as
127. The electromagnetic spectrum contains:
128. The electromagnetic waves propagated out in space from antenna of a transmitter are known as
129. The electromagnetic waves travel in space with speed of
130. The expression P = VI holds only when current and voltage are:
131. The frequency of A.C used in Pakistan is
132. The frequency of the range 20-20000 Hz is
133. The graph between time and voltage is:
134. The highest value reached by the voltage or current in one cycle is known as:
135. The highest value reached by voltage or current in one cycle is called
136. The inductive reactance of an inductor is given by
137. The inductive reactance of an inductor is given by
138. The inductive reactance of an inductor is given by
139. The instantaneous value of the A.C. voltage is given by the relation
140. The instantaneous value of the A.C. voltage is given by the relation
141. The instantaneous voltage across a pure inductance is:
142. The low frequency signal used for modulation is called:
143. The magnitude of alternating voltage is:
144. The measure of the opposition offered by a capacitor to the flow of A.C is called:
145. The minimum phase angle between V and I of RL-series circuit is
146. The most common source of A.C voltage is:
147. The most common source of alternating current is
148. The opposition offered by the inductor to the flow of A.C. is called
149. The peak value of alternating voltage is 423 volts, its rms value is:
150. The phase angle at +ve (positive) peak is
151. The phase difference between current and voltage in an Inductive circuit is
152. The positive value of current and voltage over a cycle is:
153. The power dissipated in a pure inductive or capacitive circuit is
154. The process of combining low frequency signal with high frequency radio waves is called:
155. The purpose of choke in a fluorescent lamp is:
156. The reactance is the ratio of:
157. The reactance of a coil changes directly with
158. The reactance of a coil depends upon:
159. The reactance of an inductor at 50 Hz is 10Ω its reactance at 100 Hz becomes
160. The reactance of I farad capacitance when connected to D.C circuit is:
161. The reciprocal of impedance is called:
162. The RMS value of alternating voltage is:
163. The root mean square value of the current is given as
164. The root mean square value of the current is given as
165. The SI unit of reactance is:
166. The slope of q-t curve at any instant of time gives:
167. The sum of positive and negative peak values are usually written
168. The time during which the voltage sources changes its polarity once is called:
169. The unit of impedance is:
170. The velocity of an oscillating charge as it moves to and fro along a wire is:
171. The wave form of alternating voltage is a:
172. The waveform of alternating voltage is a:
173. The waveform of alternating voltage is the graph between:
174. The waves which do not require any material medium for their propagation are called
175. Three phase supply also provides:
176. through inductor, the applied voltage:
177. To maintain the current in an inductor, the applied alternating voltage must be:
178. Voltage drop in A.C circuit is the product of current and:
179. When A.C voltage is applied to an inductor, the:
180. When A.C voltage source is connected to a capacitor:
181. When an inductor comes close to a metallic object, its inductance is:
182. When electrons in a transmitting antenna vibrate 94000 times each second, they produce radio waves having frequency
183. When resistance is increased in a series LCR circuit:
184. When voltage V and current I are in phase the power is expressed as:
185. When we accelerate the charges, which type of waves are produced
186. When XL= XCthis condition is called
187. Which consumes small power?
188. Which current can pass through a capacitor continuously:
189. Which of the following are electromagnetic waves
190. Which of the following is not electromagnetic wave in nature
191. Which of the following statement is correct for an A.C circuit:
192. Which of the following waves do not travel with speed of light
193. Who proved that light waves are electromagnetic?
194. With high frequencies, capacitive reactance:
195. With increase in frequency of an A.C supply, the impedance of LCR series circuit:
196. With increase of frequency of A.C supply, the inductive reactance is:
Short Questions
1. A circuit an iron – cored inductor a switch and a D.C source arranged in series.The switch is closed and after an interval reopened.Explain why a spark jumps across the switch contacts?
2. A sinusoidal current has rms value of 10 A.What is the maximum or peak value?
3. An inductor draws 30 ampers when connected across the terminals of generator A and 6 ampers when connected to B.Assuming the same impressed voltage can you tell which of the two generators A or B is an A.C machine?Give reasons for your answer?
4. Can electrolysis proceed with the help of an A.C source ?
5. Define alternating current (A.C) ?
6. Define direct current (D.C) ?
7. Define impedance and write its unit ?
8. Define impedence of a circuit and give its unit?
9. Define inductive reactance ?
10. Define peak value of voltage or current ?
11. Define power ?
12. Define power factor in A.C?
13. Define root mean square value (i.e. r.m.s) ?
14. Define Root Mean square value of A.C. Voltage?
15. Define time period of an alternating voltage ?
16. Describe some advantages of 3- phase A.C.supply?
17. Describe some important properties of a series resonant circuit?
18. Describe some important properties of parallel resonant circuit?
19. Describe the condition under which the reactance of a capacitor will be small ?
20. Describe the condition which will make the reactance small?
21. Describe the principle upon which the electromagnetic waves can be generated?
22. Describe the types of modulation?
23. Differentiate between Peak value and Peak to Peak value?
24. Explain the conditions under which electromagnetic waves are produced from source?
25. Explain the term peak to peak value ?
26. How an A.C flows through a capacitor ?
27. How are the radio waves received?
28. How current and voltage behave in a R-L series circuit ?
29. How current and voltage behave in an inductive circuit ?
30. How does doubling the frequency affect the reactance of (a) an inductance (b) a capacitor?
31. How many time per second will an inductance lamp reach maximum brilliance when connected to a 50Hz source?
32. How series circuit ?
33. How the out put voltage of an alternating current generator varies with time ?
34. How the radio waves are received ?
35. How the receptian of a particular radio station is selected on your radio set?
36. If 'T' is the time period of an A.C then find the frequency of an A.C ?
37. In a R- L circuit will the current lag or lead the voltage?IIIustrate your answer by a vector diagram?
38. Name a device that will (a) permit the flow of direct current but not the alternating current (b) permit alternatig current but not the direct current?
39. Name the device that will (a) permit flow of direct current but oppose the flow of alternating current.(b) permit flow of alternating current but not the direct current?
40. Name the type of modulation ?
41. Show that resonance at the resonance frequency is given as fr= 1/2πLC?
42. What are conditions for representing A.C voltage or current by vector diagram?
43. What are electromagnetic waves ?
44. What are metal detectors ?
45. What are the basic controlling elements of an A.C circuit ?
46. What are the frequencies range for an amplitude modulation transmission ?
47. What are the frequencies range for frequency modulation transmission ?
48. What are the magnitude of Vᵣₘₛ and Iᵣₘₛ respectively ?
49. What do you mean by instantaneous value ?
50. What do you mean by phase of an A.C ?
51. What do you understand about three phases A.C supply?
52. What do you understand by electromagnetic waves?
53. What do you understand by inductive reactance?
54. What do you understand by modulation and modulated carrier wave?
55. What is a choke?
56. What is a choke?Why it is used in A.C circuits?
57. What is a modulation signal ?
58. What is a power factor in an A.C circuit ?
59. What is a R-C series circuit ?
60. What is a resonance circuit ?
61. What is a R-L series circuit ?
62. What is an inductor ?
63. What is choke ?
64. What is impedance?Write its unit?
65. What is meant by A.M and F. M?
66. What is meant by electrical inertia ?
67. What is meant by frequency modulation (F.M.) ?
68. What is meant by impedence?Explain briefly.
69. What is modulation ?
70. What is peak value?
71. What is reactance of a capacitor ?
72. What is reactance?
73. What is resonance frequency of a R-L-C series circuit ?
74. What is the circuit impedance at the resonance frequency ?
75. What is the condition of resonance in a parallel resonance circuit?
76. What is the most common source of alternating voltage ?
77. What is the phase on the A.C wave form at the negative peak ?
78. What is the phase on the A.C waveform at the positive peak ?
79. What is the power through a resistor when both the current and voltage are in phase ?
80. What is the quantity of charge stored on the plates of a capacitor at any istant ?
81. What is the shape of graph for alternating voltage and time ?
82. What is the source of transmitting electromagnetic waves?
83. What is the speed of electromagnetic waves in free space ?
84. What is the type of a circuit used in metal détector ?
85. What is the use of inductor coil ?
86. What the net potential difference alternating voltage of an R-L-C series circuit ?
87. When electromagnetic discovered ?
88. Whether electromagnetic waves require a medium for transmission ?
89. Which apparatus electromagnetic waves ?
90. Why D.C can not flow through a capacitor ?
91. Write some important properties of a series resonance circuit ?
92. Write some important properties of parallel resonant circuit ?
93. Write the equation of impedance of a R-L series circuit ?
Long Questions
1. Define alternating current. Also explain time period and waveform of alternating current.
2. What is the root mean square value of alternating current?
3. Define phase of A.C. Define phase lag and phase head.
4. Describe A.C. through a capacitor.
5. Describe A.C. through an inductor.
6. Explain R.L series circuit.
7. Explain series resonance circuit also discuss its properties.
8. What is parallel resonance circuit? Describe its properties. Also find the resonance frequency for the circuit.
9. Describe the principle of metal detectors.
10. What are the electromagnetic waves?
"11. Explain the principle of generation, transmission and reception of electromagnetic waves with an example. "
12. Explain modulation with its types.
13. An alternating current is represented by the equation I = 20 sin 100 πt. Compute frequency and the maximum and r.m.s values of current.
14. A sinusoidal A.C. has a maximum value of 15 A. What are its r.m.s. values? If the time is recorded from the instant the current is zero and is becoming positive, what is the instantaneous value of the current after 1/300 s, given the frequency is 50 Hz.
15. Find the value of current and inductive reactance when A.C voltage of 220 V at 50 Hz is passed through an inductor of 10 H.
16. A circuit has an inductance of 1/π H and resistance of 2000 ohm. A 50 Hz A.C. is supplied to it. Calculate the reactance and impedance offered by the circuit.
17. An inductor of pure inductance 3/π H is connected in series with a resistance of 40 ohm. Find (i) the peak value of the current (ii) the r.m.s value, and (iii) the phase difference between the current and the applied voltage V = 350 sin (100 π t).
18. A 10mH, 20 ohm coil is connected across 240 V and 180/π Hz source. How much power does it dissipate?
19. Find the value of the current flowing through a capacitance 0.5 micro F when connected to a source of 150 V at 50 Hz.
20. An alternating source e.m.f 12 V and frequency 50 Hz is applied to a capacitor of capacitance 3 micro F in series with a resistor of resistance 1 ohm. Calculate the phase angle.
21. What is the resonant frequency of a circuit which included a coil of inductance 2.5 H and a capacitance 40 micro F?
22. An inductor of inductance 150 micro F is parallel with a variable capacitor whose capacitance can be changed from 500 pico F to 20 pico F. Calculate the maximum frequency and minimum frequency for which the circuit can be tuned.