resistance in circuits
DESCRIPTION
Supporting material for lesson on electricity (Middle or High School level).TRANSCRIPT
Resistance in Electric Circuits
Science Department
David Ramirez
2008
Resistance
• Resistance is friction that electricity experiences while flowing thru something.
• Resistance (or the lack of resistance) is used in circuits to control the flow of current.
• Symbol :
Short Circuit
Short circuit
• Very low resistance of conductors.
• This example circuit connects the poles of the voltage source together using a simple piece of wire.
• High current !
• DANGER : High conversion of energy into heat ! Burns, fire ! (don’t mess with it!).
Building fire (example of short circuit consequence)
Short circuit (conclusion)
• In a short circuit the magnitude of the current can be very large.
• The release of energy is dramatic, usually in the form of heat : melts the metal, burns insulators, can start a fire, and injuries (burns) to the man.
Simple Circuit
Simple circuit
• Normally circuits are constructed to make practical use of the released energy in a manner as safe as possible.
• One typical and practical use of a circuit is for the production of electric lighting.
Light Bulb
Light bulb (incandescent lighting)
RESISTANCE
• Electrons encounter opposition when flowing thry the filament, due to friction.
• This phenomenon is known as RESISTANCE.
• Resistance depends on material, cross section, length.
Simple electric light circuit
Bulb
Inside the light bulb
• Conductors have low resistance.• Insulators have high resistance.• Resistance limits the amount of current flowing
thru the circuit for a given voltage of the power supply.
• In the light bulb, a relatively high amount of energy is dissipated due to the resistance of the filament, and manifests as heat – so high that light is emited (filament glows).
Open circuit
Open Circuit
Breaker (switch)
Closed Circuit
• Current flows through the switch.
• Continuity is restablished.
• Light bulb glows.
KEYWORDS
• CIRCUIT• RESISTANCE• LOAD• BREAKER• SWITCH• INCANDESCENSE• CURRENT• VOLTAGE• SHORT CIRCUIT• CONTINUITY
To be continued
Units of measure (Amp, Volt, Ohm)
Ohm’s Law
Types of circuits: Series – Parallel
David RamirezJanuary, 2008
Houston ISD ACP Program