Table of contents

0. Math Review31m
- Math Review
  31m
1. Intro to Physics Units1h 29m
2. 1D Motion / Kinematics3h 56m
3. Vectors2h 43m
4. 2D Kinematics1h 42m
5. Projectile Motion3h 6m
6. Intro to Forces (Dynamics)3h 22m
7. Friction, Inclines, Systems2h 44m
8. Centripetal Forces & Gravitation7h 26m
9. Work & Energy1h 59m
10. Conservation of Energy2h 54m
11. Momentum & Impulse3h 40m
12. Rotational Kinematics2h 59m
13. Rotational Inertia & Energy7h 4m
14. Torque & Rotational Dynamics2h 5m
15. Rotational Equilibrium3h 39m
16. Angular Momentum3h 6m
17. Periodic Motion2h 9m
18. Waves & Sound3h 40m
19. Fluid Mechanics4h 27m
20. Heat and Temperature3h 7m
21. Kinetic Theory of Ideal Gases1h 50m
22. The First Law of Thermodynamics1h 26m
23. The Second Law of Thermodynamics3h 11m
24. Electric Force & Field; Gauss' Law3h 42m
25. Electric Potential1h 51m
26. Capacitors & Dielectrics2h 2m
27. Resistors & DC Circuits3h 8m
28. Magnetic Fields and Forces2h 23m
29. Sources of Magnetic Field2h 30m
30. Induction and Inductance3h 38m
31. Alternating Current2h 37m
32. Electromagnetic Waves2h 14m
33. Geometric Optics2h 57m
34. Wave Optics1h 15m
35. Special Relativity2h 10m

31. Alternating Current

Capacitors in AC Circuits

Physics

31. Alternating Current

Capacitors in AC Circuits

Previous problemNext problem

Struggling with Physics?

Join thousands of students who trust us to help them ace their exams!Watch the first video

Multiple Choice

An AC circuit consists of a capacitor and an emf source with frequency $0.25 Hz$ . If the source is turned on at $t = 0 s$ , and the first time the voltage across the capacitor reaches a maximum value is at $t = 1.4 s$ , when is the first time the current in the capacitor is at a maximum?

0.2 s

0.8 s

1.4 s

2.4 s

2.9 s

0.4 s

Previous problemNext problem

Verified step by step guidance

Understand that in an AC circuit with a capacitor, the voltage across the capacitor and the current through the capacitor are out of phase by 90 degrees (or π/2 radians). This means when the voltage is at a maximum, the current is at zero, and vice versa.

The problem states that the voltage across the capacitor reaches its maximum at t = 1.4 s. Since the voltage and current are out of phase by 90 degrees, the current will reach its maximum a quarter of a cycle before or after the voltage maximum.

Calculate the period of the AC source using the frequency. The period T is given by T = 1/frequency. With a frequency of 0.25 Hz, the period T = 1/0.25 Hz = 4 s.

Determine the time difference corresponding to a quarter of the cycle. Since the period is 4 s, a quarter of the cycle is T/4 = 4 s / 4 = 1 s.

Since the voltage maximum occurs at t = 1.4 s, the current maximum will occur 1 s before this time, which is at t = 1.4 s - 1 s = 0.4 s. Therefore, the first time the current is at a maximum is at t = 0.4 s.