This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Slide 1
Chapter 29 Continued-Chapter 31- Chapter 32
Slide 2
29-3 EMF Induced in a Moving Conductor Example 29-8: Force on
the rod. To make the rod move to the right at speed v, you need to
apply an external force on the rod to the right. (a) Explain and
determine the magnitude of the required force. (b) What external
power is needed to move the rod?
Slide 3
Electric Generators Same Principle as a motor: Motor: loop
turns due to current in B Generator: current flows due to turning
loop in B http://www.youtube.com/watch?v=zOdboRY f1hM
http://www.youtube.com/watch?v=TU8G KV2TXxo
Slide 4
A generator is the opposite of a motor it transforms mechanical
energy into electrical energy. This is an ac generator: The axle is
rotated by an external force such as falling water or steam. The
brushes are in constant electrical contact with the slip rings.
29-4 Electric Generators
Slide 5
If the loop is rotating with constant angular velocity , the
induced emf is sinusoidal: For a coil of N loops,
Slide 6
29-4 Electric Generators Example 29-9: An ac generator. The
armature of a 60-Hz ac generator rotates in a 0.15-T magnetic
field. If the area of the coil is 2.0 x 10 -2 m 2, how many loops
must the coil contain if the peak output is to be E 0 = 170 V?
Slide 7
A transformer is a device for increasing or decreasing an ac
voltage A transformer consists of two coils, either interwoven or
linked by an iron core. A changing emf in one induces an emf in the
other. The ratio of the emfs is equal to the ratio of the number of
turns in each coil: 29-6 Transformers and Transmission of
Power
Slide 8
This is a step-up transformer the emf in the secondary coil is
larger than the emf in the primary and N s > N p 29-6
Transformers and Transmission of Power
Slide 9
Energy must be conserved; therefore, in the absence of losses,
the ratio of the currents must be the inverse of the ratio of
turns: 29-6 Transformers and Transmission of Power
Slide 10
Example 29-12: Cell phone charger. The charger for a cell phone
contains a transformer that reduces 120-V ac to 5.0- V ac to charge
the 3.7-V battery. (It also contains diodes to change the 5.0-V ac
to 5.0-V dc.) Suppose the secondary coil contains 30 turns and the
charger supplies 700 mA. Calculate (a) the number of turns in the
primary coil, (b) the current in the primary, and (c) the power
transformed.
Slide 11
Transformers work only if the current is changing; this is one
reason why electricity is transmitted as ac. 29-6 Transformers and
Transmission of Power
Slide 12
A changing magnetic flux induces an electric field; this is a
generalization of Faradays law. The electric field will exist
regardless of whether there are any conductors around: 29-7 A
Changing Magnetic Flux Produces an Electric Field.
Slide 13
31-3 Maxwells Equations This set of equations describe electric
and magnetic fields, and is called Maxwells equations. In the
absence of dielectric or magnetic materials, they are:
Slide 14
Since a changing electric field produces a magnetic field, and
a changing magnetic field produces an electric field, once
sinusoidal fields are created they can propagate on their own.
These propagating fields are called electromagnetic waves (EM).
31-4 Production of Electromagnetic Waves
Slide 15
Induced Electric Fields Electric & Magnetic fields induce
each other http://www.walter-fendt.de/ph14e/emwave.htm Changing E
changing B Changing B induces emf changing E create electromagnetic
waves
Slide 16
Electromagnetic Waves Waves made of oscillating electric and
magnetic fields Produced by ACCELERATING charges E B
Slide 17
Electromagnetic Waves Charge accelerates this creates a
changing B-field By Faradays Law of induction this creates a
changing E-field E B
Slide 18
31-5 Electromagnetic Waves, and Their Speed, Derived from
Maxwells Equations B and E are related by the following equation
Here, v is the velocity of the wave..
Slide 19
31-5 Electromagnetic Waves, and Their Speed, Derived from
Maxwells Equations The magnitude of this speed is around 3.0 x 10 8
m/s precisely equal to the measured speed of light.
Slide 20
Speed of EM Waves -- vacuum EM waves do not require a medium to
propagate Permittivity of free space = 8.85 x 10 -12 C 2 /N m 2
Permeability of free space: = 4 x 10 -7 T m/A Galaxy 2 million ly
away
Slide 21
The frequency of an electromagnetic wave is related to its
wavelength and to the speed of light: 31-6 Light as an
Electromagnetic Wave and the Electromagnetic Spectrum
Slide 22
Speed of Light in matter Generally light slows down when it
encounters a medium other than vacuum. n is the index of refraction
of the medium n1 c n v Frequency is unchanged
Slide 23
Electromagnetic waves can have any wavelength; we have given
different names to different parts of the wavelength spectrum. 31-6
Light as an Electromagnetic Wave and the Electromagnetic
Spectrum
Slide 24
Chapter 32 Light: Reflection and Refraction
Slide 25
Light very often travels in straight lines. We represent light
using rays, which are straight lines emanating from an object. This
is an idealization, but is very useful for geometric optics. 32-1
The Ray Model of Light
Slide 26
Law of reflection: the angle of reflection (that the ray makes
with the normal to a surface) equals the angle of incidence. 32-2
Reflection; Image Formation by a Plane Mirror