Waves. Electromagnetic. No medium required. Can travel in a vacuum (empty space).

Transcription

1 Electromagnetic Waves Made up of vibrating electric and magnetic fields. Carry energy. Move in the form of both a wave and a particle. No medium required. Can travel in a vacuum (empty space). Demonstrate with bell in vacuum jar. tor/fundam/chapter3/08_e.php

2 The Electromagnetic Spectrum Long Wavelength Short Low Frequency High Low Energy High Speed all electromagnetic energy travels at the same speed, the SPEED OF LIGHT (in a vacuum) = 300,000 km/s (slows down when passing through a medium)

3 Bell in a vacuum jar (medium is removed) The bell cannot be heard in the vacuum because sound (mechanical waves) requires a medium to transfer its energy. The bell can be seen in the vacuum because light (electromagnetic waves) does not require a medium to travel through. Similarly, electromagnetic waves (radio waves) can travel through space, but mechanical waves (sound waves) cannot, because space is a near vacuum (there is no medium)

4 Distance = Rate X Time Earth Moon Distance = 384,000 km Electromagnetic Waves (Radio signals) travel at a rate of 300,000 km/s Why is there a delay between the time we send a radio message to astronauts on the moon and when they receive it? T=D/R (384,000km/300,000km/s) Radio signals travel at the speed of light taking 1.28 seconds to arrive at the moon causing the delay.

5 Lightning & Thunder Speed of light (all forms of e-m waves) = 300,000 km/s (in a vacuum) Avg. speed of sound in air = 340 m/s See lightening before hearing thunder. Because lightening (light) travels much faster than thunder (sound) If you saw lightening flash and it took 3 seconds for the sound of thunder to arrive, how far away did the lightening strike? Lightning would arrive to you nearly instantaneously, the sound travels 340m/s for 3s = 340 x 3 = 1020m or 1.02 km So, if you saw lightning strike and counted to 3 seconds, the lightning would be one kilometer away (0.6mi)

6 Visible Light Spectrum R O Y G B V Small portion of the EM spectrum that can be detected by our eyes. Colors are differentiated by their wavelengths (or frequencies) Electromagnetic Spectrum (EM) Wavelengths Colors on blue end of visible light spectrum have shorter wavelengths and higher frequencies. Colors on red end of visible light spectrum have longer wavelengths and lower frequencies.

7 Emit: to give off on off White light contains all the colors of the visible light spectrum ROYGBV. Without light nothing would be visible.

8 Reflect: : to bounce off The color an object appears is determined by the wavelength of light (color) it reflects. Red objects reflect red light. Green objects reflect green light.

9 Absorb: : to take in Red objects reflect red light and absorb other wavelengths.

10 White objects reflect all wavelengths of visible light. Black objects absorb all wavelengths of visible light.

11 Predict what will happen when a red light is shined on a red object. Red objects reflect red wavelengths of visible light. The green leaf on the apple absorbs the red light, so it appears black. Yellow light is not emitted by the red light so the yellow ball appears black because no yellow light is reflected. The red light is absorbed.

12 Refract: : to bend Predict what will happen when the transparent straw is placed in the beaker of water. The straw appears larger and it appears to bend. This is due to the light that is reflecting off the straw is refracted (bent) as it changes mediums (from the water to the air).

13 Transmit: : to pass through Ex. A window allows light to pass through it.

14 White Light Yellow filter

15 Scatter: : to spread out The surface of the wall is rough. The wall appears green because green light is reflected and scattered off the wall. The other colors are absorbed by the wall.

16 Scatter: : to spread out The white light is being refracted and scattered by the prism. Blue light is scattered the most because it has the smallest wavelength. Red light is scattered the least because it has the longest wavelengths. A prism

17 Additive Primary Colors In equal amounts white light is produced When added they can produce any color in the visible light spectrum

18 Subtractive Primary Colors When mixed, the color seen is the color that survives the subtraction When mixed, they reflect any color in the visible light spectrum

19 Complementary Colors Two colors that produce white light when added

20 Why is the sky blue? Sunlight contains the full visible light spectrum. N N O O The shortest wavelengths of visible light are blue/violet which are nearly the same size as a molecule of oxygen or nitrogen in Earth s atmosphere. This causes the blue light to be scattered the most, giving our atmosphere its blue color. The other wavelengths are not affected, traveling straight to our eyes. The remaining colors together give the Sun its yellow appearance.

21 Why does the Sun appear reddish at sunrise / sunset? Sun at noon angle At sunrise and sunset, sunlight travels through more atmosphere, scattering more of the shorter wavelength light. The remaining light gives the Sun its reddish appearance. Molecules in Earth s atmosphere scatter the shortest wavelengths of sunlight. Less atmosphere to transmit through Sun at sunrise / sunset angle More atmosphere to transmit through