Docsity
Docsity
Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity

Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips
Guidelines and tips
Sell on Docsity
Sell on Docsity
Docsity AI
Docsity AI
Log inSign up

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search for your university

Find the specific documents for your university's exams

Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents
download point icon20 Points

For each uploaded document

Answer questions
download point icon5 Points

For each given answer (max 1 per day)

All the ways to get free points
Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

Lecture Slides on Flashlights - How Things Work | PHYS 140, Study notes of Classical Physics

University of Illinois - Urbana-ChampaignClassical Physics

Material Type: Notes; Class: How Things Work; Subject: Physics; University: University of Illinois - Urbana-Champaign; Term: Unknown 1989;

Typology: Study notes

Pre 2010

Uploaded on 03/16/2009

koofers-user-4ea-1
koofers-user-4ea-1 🇺🇸

10 documents

1 / 6

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
•1
10.3 Flashlights
10.3 Flashlights Observations About Flashlights
Observations About Flashlights
• They turn on and off with a switch
• More batteries usually means brighter
• Orientation of multiple batteries matters
• Flashlights dim as batteries age
Click me
A Battery
A Battery
• Battery “pumps” electrons from – end to + end
(outside of the battery)
– Chemical potential energy is consumed
– Electrostatic potential energy is produced
• In the battery:
The current undergoes a rise in voltage
– Alkaline cell: 1.5 volt rise
– Lead-acid cell: 2.0 volt rise
– Lithium cell: 3.0 volt rise
• Chain of cells produces larger voltage rise
pf3
pf4
pf5

Partial preview of the text

Download Lecture Slides on Flashlights - How Things Work | PHYS 140 and more Study notes Classical Physics in PDF only on Docsity!

10.3 Flashlights 10.3 Flashlights

Observations About FlashlightsObservations About Flashlights

  • They turn on and off with a switch
  • More batteries usually means brighter
  • Orientation of multiple batteries matters
  • Flashlights dim as batteries age

Click me

A Battery A Battery

  • Battery “pumps” electrons from – end to + end (outside of the battery)
  • Chemical potential energy is consumed
  • Electrostatic potential energy is produced
  • In the battery: The current undergoes a rise in voltage - Alkaline cell: 1.5 volt rise - Lead-acid cell: 2.0 volt rise - Lithium cell: 3.0 volt rise
  • Chain of cells produces larger voltage rise

A Light BulbA Light Bulb

  • Filament barely lets charge flow through it
    • Electrostatic potential energy is consumed
    • Thermal energy is produced
    • It’s a resistor!
  • Current undergoes a drop in voltage
    • Two-cell alkaline flashlight: 3.0 volt drop

A Simple CircuitA Simple Circuit

  • A battery – the energy source
  • A wire – the outgoing current path
  • A light bulb – the energy destination (the load)
  • A wire – the return current path

Clicker Question:Clicker Question:

If you remove the 2 batteries from a working flashlight and reinstall them backward so that they make good contact inside, will the flashlight still work? A. Yes B. No

Circuits 1Circuits 1

  • Steady current requires a circuit path (loop)
    • Charge mustn’t accumulate anywhere
    • Closed conducting loop avoids accumulation
  • Steady current flow requires energy
    • Currents lose energy (and voltage) in conductors
    • Missing energy becomes thermal energy
    • Lost energy must be replaced

Circuits 2 Circuits 2

  • A circuit can transport energy
    • Current obtains energy from a battery
    • Current delivers energy to a light bulb
    • Current starts the trip over again

Voltages Add:Voltages Add:

Short Circuits Short Circuits

  • If a conducting path bridges the load - Current bypasses the load - Circuit is abbreviated or “short”
  • No appropriate energy destination (load)
  • Energy loss and heating occurs in the wires
  • A recipe for fires!
    • The currents passing through most wires and other devices experience voltage drops
    • In an “ohmic device,” the voltage drop is proportional the current: voltage drop = resistance · current

V = I × R

where resistance is a constant for the device

OhmOhm’’s Law (V=I x R)s Law (V=I x R)

Clicker Question:Clicker Question:

Why can a bird safely stand on a power line? A. The bird does not make a complete circuit with the power line – it would have to have each leg on different lines. B. Power lines are insulated. C. The resistance of the bird is much higher than the power line.