<< Chapter < Page Chapter >> Page >

Making connections: conservation of energy

Lenz’s law is a manifestation of the conservation of energy. The induced emf produces a current that opposes the change in flux, because a change in flux means a change in energy. Energy can enter or leave, but not instantaneously. Lenz’s law is a consequence. As the change begins, the law says induction opposes and, thus, slows the change. In fact, if the induced emf were in the same direction as the change in flux, there would be a positive feedback that would give us free energy from no apparent source—conservation of energy would be violated.

Calculating emf: how great is the induced emf?

Calculate the magnitude of the induced emf when the magnet in [link] (a) is thrust into the coil, given the following information: the single loop coil has a radius of 6.00 cm and the average value of B cos θ size 12{B"cos"θ} {} (this is given, since the bar magnet’s field is complex) increases from 0.0500 T to 0.250 T in 0.100 s.

Strategy

To find the magnitude of emf, we use Faraday’s law of induction as stated by emf = N Δ Φ Δ t , but without the minus sign that indicates direction:

emf = N Δ Φ Δ t .

Solution

We are given that N = 1 size 12{N=1} {} and Δ t = 0 . 100 s , but we must determine the change in flux Δ Φ size 12{ΔΦ} {} before we can find emf. Since the area of the loop is fixed, we see that

Δ Φ = Δ ( BA cos θ ) = A Δ ( B cos θ ). size 12{ΔΦ=Δ \( BA"cos"θ \) =AΔ \( B"cos"θ \) } {}

Now Δ ( B cos θ ) = 0 . 200 T size 12{Δ \( B"cos"θ \) =0 "." "200"`T} {} , since it was given that B cos θ size 12{B"cos"θ} {} changes from 0.0500 to 0.250 T. The area of the loop is A = πr 2 = ( 3 . 14 . . . ) ( 0 . 060 m ) 2 = 1 . 13 × 10 2 m 2 size 12{A=πr rSup { size 8{2} } = \( 3 "." "14" "." "." "." \) \( 0 "." "060"`m \) rSup { size 8{2} } =1 "." "13" times "10" rSup { size 8{ - 2} } `m rSup { size 8{2} } } {} . Thus,

Δ Φ = ( 1.13 × 10 2 m 2 ) ( 0.200 T ). size 12{ΔΦ= \( 1 "." "13" times "10" rSup { size 8{ - 2} } " m" rSup { size 8{2} } \) \( 0 "." "200"" T" \) } {}

Entering the determined values into the expression for emf gives

Emf = N Δ Φ Δ t = ( 1.13 × 10 2 m 2 ) ( 0 . 200 T ) 0 . 100 s = 22 . 6 mV. size 12{E=N { {ΔΦ} over {Δt} } = { { \( 1 "." "13" times "10" rSup { size 8{ - 2} } " m" rSup { size 8{2} } \) \( 0 "." "200"" T" \) } over {0 "." "100"" s"} } ="22" "." 6" mV"} {}

Discussion

While this is an easily measured voltage, it is certainly not large enough for most practical applications. More loops in the coil, a stronger magnet, and faster movement make induction the practical source of voltages that it is.

Phet explorations: faraday's electromagnetic lab

Play with a bar magnet and coils to learn about Faraday's law. Move a bar magnet near one or two coils to make a light bulb glow. View the magnetic field lines. A meter shows the direction and magnitude of the current. View the magnetic field lines or use a meter to show the direction and magnitude of the current. You can also play with electromagnets, generators and transformers!

Faraday's Electromagnetic Lab

Section summary

  • Faraday’s law of induction states that the emf induced by a change in magnetic flux is
    emf = N Δ Φ Δ t size 12{"emf"= - N { {ΔΦ} over {Δt} } } {}

    when flux changes by Δ Φ size 12{ΔΦ} {} in a time Δ t size 12{Δt} {} .

  • If emf is induced in a coil, N is its number of turns.
  • The minus sign means that the emf creates a current I size 12{I} {} and magnetic field B size 12{B} {} that oppose the change in flux Δ Φ size 12{ΔΦ} {} —this opposition is known as Lenz’s law.

Conceptual questions

A person who works with large magnets sometimes places her head inside a strong field. She reports feeling dizzy as she quickly turns her head. How might this be associated with induction?

A particle accelerator sends high-velocity charged particles down an evacuated pipe. Explain how a coil of wire wrapped around the pipe could detect the passage of individual particles. Sketch a graph of the voltage output of the coil as a single particle passes through it.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply
Practice Key Terms 2

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, College physics (engineering physics 2, tuas). OpenStax CNX. May 08, 2014 Download for free at http://legacy.cnx.org/content/col11649/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics (engineering physics 2, tuas)' conversation and receive update notifications?

Ask