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Chapter 19

PHY152H1 Chapter Notes - Chapter 19: Series And Parallel Circuits, Internal Resistance, Electric Potential


Department
Physics
Course Code
PHY152H1
Professor
Young- June Kim
Chapter
19

Page:
of 5
Electrical Currents
Electrical potential dierence, current + resistance
+ has a higher PE
Current: flow of charge per unit time
current flows from + —> -
Amp is a scalar quantity
Electrons are negative so they flow from - to +
Battery:
chemical energy —> electrical energy
charges rearranged so that there are more + charges at the + end
Potential dierence: work done per unit charge
Resistance: rate of flow of charge
flow of electrons through metal give energy to metal atoms, causing temp of metal to
increase
Ohm’s law: current flowing through an ohmic conductor is directly proportional to the
potential dierence across it, provided temp + physical conditions remain constant
Non-ohmic conductors e.g. light bulb
light bulb gets hot —> metal atoms vibrate more —> more collisions between
metal atoms + electrons—> increase resistance
Electric currents
emf: amount of chemical energy converted to electrical energy per unit charge (specific
to cells, batteries + generators)
Potential dierence: amount of electrical energy converted to thermal energy per unit
charge
1 volt= 1 joule per couloub
Law of conservation of energy: energy converted from chemical —> electrical in the
cell is equal to the energy converted from electrical —> heat in resistor
Internal resistance: resistance of a cell
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Electrical power: rate at which energy is changed from one form to another
Power (battery): amount of chemical energy converted to electrical energy per unit
time
Series circuit:
Resistors:
same current
VT=V1+ V2
RT=R1 +R2
Cells:
VT=V1+V2
Parallel circuit:
Resistors:
same voltage
IT=I1 + I2
1/RT=1/R1 + 1/R2
Electrical measurements
voltage: voltmeter- digital + analogue
ideal voltmeter= infinitely high resistance so it doesn’t take any current from the
circuit
current= ammeter
Ideal ammeter= 0 resistance so it doesn’t change the current in the circuit
Electrical sensors: a device whose electrical properties change with changing physical
conditions
Thermistor
semiconducting material
resistance decreases as temp increases
increase in temp causes the release of more charge carries —> current
can flow more easily
Light sensor (LDR)
light dependent resistor
semiconducting device
light releases more charge carries resulting in lower resistance
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find more resources at oneclass.com
Strain gauge
thin metal wire
stretch —>length increases —> cross-sectional area gets smaller —
> increase in resistance
Potential divider:
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find more resources at oneclass.com