Lecture Notes: Intensity in Waves and Physics

Introduction

• Focus on understanding the concept of intensity in waves.
• Intensity = Energy per second per unit area.
• Measured in watts per meter squared (W/m²).

Basic Concepts

• Intensity (I): Power divided by area.
• Power is energy per second (measured in watts).
• Example: Intensity of sunlight is high in a desert compared to a cloudy day.

Intensity and Distance

• Intensity decreases with distance from the source.
• Energy spreads over a larger area as distance increases.
• Example: TV signal weaker further from the transmitter.

Sound Waves

• Intensity of sound decreases with distance.
• Energy spreads over the surface area of a sphere.

Mathematical Explanation

• Shining a torch on a card shows intensity decreases as distance increases.
• Reading Example: A light meter reads 800 at 30 cm, 200 at 60 cm.
• Inverse Square Law: Intensity is proportional to 1/(distance)².

Calculations

• Formula: I = K / R²
  • K is a constant, I is intensity, R is distance.
• Doubling Distance: Intensity is a quarter.
• Tripling Distance: Intensity is a ninth.

Problem-Solving

• Calculate intensity at different distances given a value of K.
• Example Problem:
  • At 30 cm: Intensity is 6.6
  • At 60 cm: Intensity becomes 1.65
  • Calculate K and use it for further distances.

Exam Question Example

• Given: At 1 meter, intensity is 100 W/m².
• Required: Calculate the distance where intensity is 30 W/m².
• Solution involves finding K and rearranging the formula.
  • R = √(K/I)
  • Solve for R with K = 100, I = 30.

Conclusion

• Intensity follows inverse square law in wave physics.
• Understanding and calculation of intensity are crucial in applied science contexts.
• Practice with formulas and problem-solving is essential for mastering the concept.