Transcript EM-4 circuit Powerpoint

Chapter 34 and Chapter 35

Circuit-Pathway for current


Current-The rate at which a positive charge
moves through a wire
Voltage-The energy needed to move a
charge

Direct current (DC)-Current traveling in 1
direction (from pos. to neg.)


Example: battery
Alternating current (AC)-Current that
travels 1 way and then the other

Current changes from pos. to neg. and back to pos.
60 times a second

The current flowing in a wire is directly
proportional to the voltage across the
circuit and inversely proportional to the
resistance in the circuit


More potential difference (voltage)=more current
More resistance=less current


V=IR
V=Voltage (V)-potential difference (build up
of electrons)


What supplies the “push” that makes current
move (like the water behind a dam or pressure
supplied by a pump)
Shown as…


V=IR
I=current (A)-the rate of flow of charge for
the conventional (positive) current

Like water in pipes or a hose


V=IR
R=resistance (Ω called Ohms)-Opposes
the flow of current


Like a kink in a hose
Shown as….

What is the resistance of an electric frying
pan that draws 12 amperes of current when
connected to a 120 volt circuit?

If the resistance of your body were 100,000
ohms, what would be the current in your
body when you touched the ends of a 12 volt
battery?



Resistivity of the material
Area the current flows through
Length the current must travel





R= ρl/A
R=resistance (Ω)
ρ=resistivity (Ωm)-depends on material
l=length (m)
A=cross sectional area (m²)

Area of circle: A=лr²

The resistivity of copper is 1.76 X 10^-8
Ωm. What is the resistance of a coil of
copper wire of total length 5.5 m and
diameter of .0041 m?

What is the resistance of a coil of copper
wire that is 5 m long and has a resistivity of
2.5 X 10^-5 Ωm if the radius of the wire is
0.02m?


What happens to the resistance when:
The length of the wire increases?


Resistivity increases?


Resistance increase
Resistance increases
Area increases?

Resistance decreases

Open circuit-An “opening” or break in the
wire causing NO current to flow


Example: Turning a switch off
Closed circuit-A continuous wire allowing
current to flow

Example: Turning a switch on

Series circuit-2 or more resistors in the
same wire (without a split in the wire)


Only 1 path for the current to go
Christmas lights example



The resistance in a circuit is the sum of the
individual resistances (R Total=R1+R2+R3+..)
The battery voltage is the sum of the
voltages (Voltage Total=V1+V2+V3+…..)
The current is the same everywhere in the
circuit (I total=I1=I2=…)

Use Ohm’s Law



Parallel circuit-2 or more resistors in a
circuit on different wires (split wire)
2 or more paths for the current to go with ONLY 1
resistor in each path
Christmas lights: What happens when 1 light
goes out?



The total current is the sum of the
individual currents (I Total=I1+I2+I3+…)
The voltage is the same throughout the
circuit (V Total=V1=V2=V3=…)
The total resistance in a circuit is the sum
of the individual resistances
(1/RT = 1/R1 + 1/R2 + 1/R3 +…)

Combination circuit-Series circuit + parallel
circuit

Ammeter-an electrical instrument used to
measure current



Low internal resistance
Connected in “series” (in-line) with other circuit
elements
Voltmeter-measures the voltage in a parallel
circuit


High internal resistance
Connected “in parallel” (across) other circuit
elements

Power (W or “watts”)-The rate which energy
is produced or consumed


Turned from one form into another
Example: Current to heat

Power=IV

P=I²R

What is the total power of the resistors in a
wire that has a current of 3.5 A and a total
resistance of 34.3Ω?