MDCAT XI Physics Electronics + AC Current Online Test-2

Created on July 26, 2025 By

📚 Test Details

Subject: Physics
Class: 1st year / XI
Chapter: Electronics + AC Current
Test: 2
Book: Sindh Textbook
Total No. Of MCQs: 25 MCQs
Time Allowed: 25 Minutes

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1 / 50

1. In an AC circuit, when current reaches its maximum value before voltage, it is called:

a) Phase lag

b) Phase lead

c) Resonance

d) Rectification

2 / 50

2. Phase difference between voltage and current in a pure resistive circuit is:

a) 90°

b) 0°

c) 180°

d) 270°

3 / 50

3. Which of the following devices causes the current to lag behind voltage in an AC circuit?

a) Resistor

b) Capacitor

c) Inductor

d) Diode

4 / 50

4. Phase lag in an AC circuit means:

a) Voltage is zero

b) Current is leading voltage

c) Current reaches its peak after voltage

d) Voltage and current are equal

5 / 50

5. In a circuit containing only a resistor and AC source, the current:

a) Leads the voltage

b) Lags behind voltage

c) Is in phase with voltage

d) Is zero

6 / 50

6. In a capacitive AC circuit, the current leads the voltage by:

a) 90°

b) 45°

c) 0°

d) 180°

7 / 50

7. What happens to the capacitive reactance when frequency increases?

a) Increases

b) Decreases

c) Remains the same

d) Becomes zero

8 / 50

8. The inductive reactance of a coil is directly proportional to:

a) Resistance

b) Capacitance

c) Frequency

d) Current

9 / 50

9. Impedance in an RLC series circuit is minimum when:

a) XL = XC

b) XL > XC

c) XC > XL

d) No resonance

10 / 50

10. Unit of inductive reactance is:

a) Henry

b) Ohm

c) Farad

d) Volt

11 / 50

11. Which component opposes the change in current in an AC circuit?

a) Resistor

b) Capacitor

c) Inductor

d) Transistor

12 / 50

12. At resonance, the voltage and current in an RLC series circuit are:

a) Out of phase

b) In phase

c) Zero

d) Infinite

13 / 50

13. In an AC circuit, the average power consumed by a pure capacitor is:

a) Maximum

b) Zero

c) Negative

d) Equal to voltage

14 / 50

14. What is the main advantage of AC over DC in transmission?

a) Constant voltage

b) Low cost of wires

c) Easy to transform voltage

d) No need of batteries

15 / 50

15. If frequency is doubled in an AC circuit, the inductive reactance becomes:

a) Half

b) Double

c) Same

d) Zero

16 / 50

16. Which of the following has the longest wavelength?

a) Gamma rays

b) Infrared

c) Radio waves

d) X-rays

17 / 50

17. Which electromagnetic wave is commonly used in medical imaging?

a) Ultraviolet

b) X-rays

c) Infrared

d) Microwaves

18 / 50

18. The electromagnetic spectrum is arranged in order of:

a) Increasing density

b) Increasing speed

c) Increasing frequency

d) Random order

19 / 50

19. Gamma rays are produced in:

a) Radio stations

b) Nuclear reactions

c) Electric circuits

d) TV remotes

20 / 50

20. The process of converting AC to DC is called:

a) Amplification

b) Rectification

c) Modulation

d) Differentiation

21 / 50

21. In a half-wave rectifier, the output is obtained:

a) During both cycles

b) Only in positive half-cycle

c) Only in negative half-cycle

d) Continuously

22 / 50

22. A full-wave rectifier gives:

a) Pure DC

b) Pulsating DC

c) Alternating output

d) Zero output

23 / 50

23. Which component is essential in a rectifier circuit?

a) Transformer

b) Diode

c) Inductor

d) Transistor

24 / 50

24. Advantage of full-wave over half-wave rectifier is:

a) Smaller output

b) Uses more diodes

c) More efficient DC output

d) Works only on low voltages

25 / 50

25. In a bridge rectifier, how many diodes are used?

a) 1

b) 2

c) 4

d) 6

26 / 50

26. A PN junction diode conducts current only when:

a) Reverse biased

b) Forward biased

c) At zero bias

d) Cut-off mode

27 / 50

27. In reverse bias, the PN junction:

a) Allows current flow

b) Blocks current flow

c) Operates like a resistor

d) Emits light

28 / 50

28. The depletion region in a diode acts like a:

a) Conductor

b) Insulator

c) Power source

d) Capacitor

29 / 50

29. For light detection, a photodiode is used in:

a) Forward bias

b) Reverse bias

c) No bias

d) Breakdown mode

30 / 50

30. Which of the following devices emits light when forward biased?

a) Photodiode

b) Transistor

c) LED

d) Zener diode

31 / 50

31. Transformers are used in:

a) DC circuit only

b) AC circuit only

c) Both AC and DC

d) None

32 / 50

32. An inductor, a resistor and a capacitor are used in series with an AC source. As the frequency of the source increased from very low , the resistance:

a) Of inductor increase

b) Of resistor increase

c) Of capacitor increase

d) Of circuit increase

33 / 50

33. A capacitor acts as an infinite resistance for:

a) DC

b) AC

c) Both AC and DC

d) None

34 / 50

34. In an AC circuit, the phase relationship between resistor voltage and capacitor voltage is:

a) Resistor voltage leads by 90°

b) Resistor voltage lags by 180°

c) Both voltages are in phase

d) The voltages are 360° apart

35 / 50

35. Resonant frequency is the frequency at which

a) Current becomes zero

b) Impedance is at maximum

c) Voltage stops oscillating

d) Impedance is at minimum

36 / 50

36. A 50 Hz AC signal is applied to a capacitor. If C = 10 µF, what is the capacitive reactance

a) 200 ohm

b) 50 ohm

c) 318 ohm

d) 150 ohm

37 / 50

37. If the frequency of an AC signal is doubled, the capacitive reactance (Xc) will:

a) Double

b) Halve

c) Remain constant

d) Quadruple

38 / 50

38. What is the phase difference between voltage and current in a pure inductor

a) 0°

b) 45°

c) 90°

d) 180°

39 / 50

39. For a half wave rectification, the input frequency is

a) equals one-half of the output frequency

b) equals to the output frequency

c) equals two times of the output frequency

d) is three times the output frequency

40 / 50

40. The energy gap between the valance and conduction band of silicon is

a) 1.1 eV

b) 0.72 eV

c) 1.7 ×10^{-19 J}

d) both a and c

41 / 50

41. What is the function of a diode in an electrical circuit?

a) Converts AC to DC

b) Ensures unidirectional flow of current

c) Amplifies the current

d) Stores electrical energy

42 / 50

42. Why is the current very small in a PN junction under reverse bias?

a) Because the depletion region becomes thicker and more resistive

b) Because electrons flow freely across the junction

c) Because the PN junction becomes forward biased

d) Because holes and electrons combine rapidly

43 / 50

43. How does forward biasiing affect the depletion region and current flow in PN junction?

a) widens the depletion region, decreases the current flow

b) Narrows the depletion region and increases the current flow

c) Breaks the junction completely

d) Converts AC to DC

44 / 50

44. A completely filled band is called

a) conduction

b) firm

c) valance

d) forbidden

45 / 50

45. Acceptor impurities are

a) germanium, silicon

b) indium, gallium

c) antimony, arsenic

d) diamond, carbon

46 / 50

46. a half-wave rectifier the diode conducts during

a) both halves of the input cycle

b) a portion of the positive half of the input cycle

c) a portion of the negative half of the input cycle

d) One half of the input cycle

47 / 50

47. A standard full wave bridge rectifier contains how many diodes

a) 2 diodes

b) 4 diodes

c) 6 diodes

d) depends upon input voltage

48 / 50

48. In full wave rectification, the output D.C. voltage across the load is obtained for

a) The positive half cycle of input A.C

b) The negative half cycle of input A.C

c) The complete cycle of input A.C

d) All of the above

49 / 50

49. Rectification is possible by

a) Transistor

b) Amplifier

c) Diode

d) Capacitor

50 / 50

50. In forward bias , the depletion region of PN junction behaves like:

a) A insulator

b) A semiconductor

c) A conductor

d) All of these

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MDCAT XI Physics Electronics + AC Current Online Test-2

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