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 100 W lightbulb actually emits around only 10 W of light. What is the intensity of the light 1 cm away if the light is emitted perfectly spherically? What is the magnitude of the electric field emitted by the lightbulb? What about the magnetic field?

Intensity = 318 W/m²; Electric field intensity = 489 N/C; Magnetic field intensity = 1.63μT

Intensity = 7958 W/m²; Electric field intensity = 2448 N/C; Magnetic field intensity = 8.16μT

Intensity = 31830 W/m²; Electric field intensity = 4897 N/C; Magnetic field intensity = 16.3μT

Intensity = 7958 W/m²; Electric field intensity = 2448 N/C; Magnetic field intensity = 2.17 μT

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Verified step by step guidance

First, calculate the intensity of the light at a distance of 1 cm from the lightbulb. Intensity (I) is defined as the power (P) per unit area (A). Since the light is emitted spherically, the area is the surface area of a sphere with radius r. Use the formula: I = P / A, where A = 4πr².

Convert the distance from centimeters to meters for consistency in units. Since 1 cm = 0.01 m, the radius r = 0.01 m.

Substitute the given power of the light (10 W) and the calculated area into the intensity formula: I = 10 W / (4π(0.01 m)²).

Next, calculate the magnitude of the electric field (E) using the relationship between intensity and electric field: I = (1/2)ε₀cE², where ε₀ is the permittivity of free space (8.85 x 10⁻¹² C²/N·m²) and c is the speed of light (3 x 10⁸ m/s). Rearrange the formula to solve for E: E = sqrt(2I / (ε₀c)).

Finally, calculate the magnitude of the magnetic field (B) using the relationship between the electric field and magnetic field in an electromagnetic wave: B = E / c. Substitute the calculated electric field value to find B.