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

32. Electromagnetic Waves

Intensity of EM Waves

Physics

32. Electromagnetic Waves

Intensity of EM Waves

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Multiple Choice

A $50 W$ light bulb emits light uniformly in all directions. What is the electric field amplitude $10 cm$ away from the light bulb?

640 V / m

700 V / m

870 V / m

980 V / m

1100 V / m

550 V / m

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Verified step by step guidance

Understand that the power of the light bulb is given as 50 W, and it emits light uniformly in all directions, which means it can be treated as a point source radiating spherically.

Recall that the intensity (I) of the light at a distance (r) from a point source is given by the formula: I = P / (4πr²), where P is the power of the source.

Substitute the given values into the intensity formula: P = 50 W and r = 0.1 m (since 10 cm = 0.1 m). Calculate the intensity at this distance.

The intensity is related to the electric field amplitude (E) by the formula: I = (1/2)ε₀cE², where ε₀ is the permittivity of free space and c is the speed of light. Rearrange this formula to solve for E.

Substitute the calculated intensity and known constants (ε₀ and c) into the rearranged formula to find the electric field amplitude E at 10 cm from the light bulb.