Ch. 22 Electromagnetic Waves

what is the difference between radio waves and x-rays?

both are electromagnetic waves

• differ in frequency/wavelength

• x-rays = protons

What does Gauss’s Law say in terms of electric fields

electric fields produced by electric charges

What does Gauss’s Law say in terms of magnetic fields

there are no magnetic “charges”

What does Faraday’s law state?

changing magnetic field induces electric field

What makes ampere-Maxwell’s law different?

magnetic field produced by:

• electric current

• change in electric field

A changing electric field produces what

a mangetic field

How is a magnetic field produced?

by an electric current and by changing electric field

What did Ampere’s Law originally say and what was the problem with it?

original: magnetic fields circulate around electric currents

• problem = not true for capacitors

  • current flows in wire and up to plates so NOT through the gap between the plates

    • aka something else is present (displacement current)

in between plates of a capacitor, what is found? What is this and law does this fix?

• find displacement current

  • new current between plates of capacitor

  • its a “fake current” caused by a changing electric field”

    • keeps the magnetic field going even though it isn’t truly a flowing current (between the w plates)

• fixes Ampere’s Law

Can displacement current be changed? if so, how?

• can change electric field/current by charging capacitor

what is electric flux?

how much electric field is passing through an area

What 2 ways can change in regards to creating displacement current?

• changing the area the field goes through

• changing the electric field

How are electromagnetic fields produced?

created when:

• electric field produces a magnetic field

• changing magnetic field produces electric field

• CREATE sinusoidal fields they propogate on their own

  • propogated fields = “electromagnetic fields

How does a switch relate to the electric/magnetic fields?

open switch

• no current = no fields

closed switch

• current flows

• generate electric & magnetic fields

When there is a closed switch, what happens as the fields are trying to stabilize?

• takes time to stabilize, so they:

  • travel at speed of light

  • radiate outward (go far)

What happens to the fields when the battery is replaced with an AC source?

• (+)/(-) alternate

• current reverses the direction which makes electric/magnetic fields alternative too

  • causes waves to form away from source

In an electromagnetic wave, how are the electric and magnetic fields oriented?

• perpendicular to each other and perpendicular to direction of travel

True or False: visible light plays a HUGE part of the electromagnetic wave

False = small part****

Electromagnetic waves behave like _____

Electromagnetic waves behave like VISIBLE LIGHT

Can energy be carried/stored by ONLY the magnetic field?

No,

• by magnetic AND electric field

________ is energy per area per time, but what is constantly changing?

INTENSITY, but E/B constantly change

Besides energy, waves also carry what?

carry momentum (p)

True or False: when light strikes an object it can only be considered as being absorbed.

false

• can be considered as absorbed or reflected

What are the two types of frequencies that radios use to communicate?

• FM (88-108)

• AM (530 - 1700)

What are tuning circuits used for?

to help antennas recieve a signal by choosing the right requency by using:

• capacitors

• inductors

• transistors

True or False: antennas can detect magnetic and/or electric fields.

true