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The potential difference (voltage) is 1.5 V for a battery.

Voltage•the measure of energy•measure of “potential differenceThe unit for voltage is volts (V)

The higher the energy, the greater the voltage (potential difference).

Potential difference flows from high energy to low energy

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Current is the raterate of the flow of an electrical charge.

++

How

fast is

this

wate

r com

ing

ou

t?

How fast (speed) is the electricity flowing through these wires?

CURRENT (I) is measured in Amperes or Amps CURRENT (I) is measured in Amperes or Amps (A).(A).

3

Resistance (R) is measured in ohms.Resistance (R) is measured in ohms.

The slowing down or stopping of current.

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ResistanceResistance

CurrentCurrent

VoltageVoltage

How Fast?How Fast?

How much?How much?

How much is it How much is it slowed down?slowed down?

Match the word on the left to the phrase on the Match the word on the left to the phrase on the right.right.

(R) in Ohms

(I) in Amps

(V) in Volts

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Electrical Measuring Instruments

• Voltmeter-used in parallel to measure voltage

• Ammeter-used in series to measure current

• Galvanometer-used to detect a current

• Ohmmeter-measures resistance

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We can use this formula to figure We can use this formula to figure out voltage, current and resistance.out voltage, current and resistance.

Georg Simon Ohm

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Ohm’s Law Information

• If voltage goes up, the charges move a little faster between atoms and we get more current.

•Resistance of metals increases with temperature, because the particles collide more often causing more resistance.

•A current vs. voltage graph shows us if resistance changes.

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Calculating Ohms Law

Divide

Multiply

V

volts

Iamps

Rohms

And, to find Resistance, we need to DIVIDE voltage by current.

R = V I

So, to find Current, we need to divide voltage by resistance.

I = V / R

I = V / R

To find voltage we multiple current and resistance. V = IR

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Calculate the potential difference (voltage) across a 3 resistor if a 0.5 A current is flowing through it.

I = V / R

What do you know?What do you know?

V =I =

R =

0.5 A

3

??

V = 3 0.5 A x

VV=1.5 Volts

10

A radio with a resistance of 240 is plugged into a 120 V outlet. What is the current flowing from the outlet?

I = V / R

What do you know?What do you know?

V =I =

R =

120 V

240

??

0.5 amps0.5 amps= I

I = 120 / 240

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Do the Practice Problem

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Electrical Poweris rate at which energy flows

Power = current x voltage

Power (P) is measured in Watts (W)

P = I x V

Divide

Multiply

P

I V

watts

amps

volts

So, to find Current, we need to DIVIDE power by voltage.

I = P V

And, to find Voltage, we need to DIVIDE power by current.

V = P I

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Where do Power Units come from?

Power = Voltage x Current

Joules Joules Coulomb

second Coulomb second

(Watts) (volts) (amps)

= x

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Electrical Power ProblemIf a CD player uses 4.5 V with 0.2 amps of

current, what is the power it uses?

P =I =

V =

0.2 A

4.5 V

?? P =0.2 A x 4.5 V

P = 0.9 Watts

P= I x V

Do the Practice Problem

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16

Electrical Energy

Electrical Energy = power x time

Is measured in kilowatt-hoursKilo means 1000x

E = P x t

Divide

Multiply

E

kWhr

P

kW

t

hr

So, to find power, we need to DIVIDE energy by time.

P = E t

And, to find time, we need to DIVIDE energy by power.

t = E P

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Electrical Energy Problem

• You use your hairdryer for 10 minutes everyday. The hairdryer uses 1000 watts. How many kilowatt-hours does your hairdryer use in 12 days?

E =P =t =

1000 W = 1 kW10min / 60 = 0.17 hr

E = 1 kW x 0.17 hr

0.17 x 12 days= 2 kWhr0.17 x 12 days= 2 kWhr

E = P x t

Do the Practice Problems

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