Electric current
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Electric Current. Section 1-3. Intro: Take out a sheet of paper for today’s notes Draw the following diagram and label the parts. Open Switch. Conductor. Closed Switch. +. Battery. Load. -. A light is an example of a load. Fuse. Basic Circuit. Resistor. Open Switch.

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Electric Current

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Electric current

Electric Current

Section 1-3


Intro take out a sheet of paper for today s notes draw the following diagram and label the parts

Intro:Take out a sheet of paper for today’s notesDraw the following diagram and label the parts

Open Switch

Conductor

Closed Switch

+

Battery

Load

-

A light is an example of a load

Fuse

Basic Circuit

Resistor


Intro take out a sheet of paper for today s notes draw the following diagram and label the parts1

Open Switch

Intro:Take out a sheet of paper for today’s notesDraw the following diagram and label the parts

Closed Switch

Conductor

+

Battery

Load

-

Fuse

Resistor

Write in your notes: A circuit must be closed to have electrons flow (current) and the load on


Lights on lights off

Lights on Lights off

An open circuit is off


Lights on lights off1

Lights on Lights off

A closed circuit is on


What electrons really do

What electrons really do

  • Electrons move slowly bouncing around in many directions as they move in one direction overall.

Draw the picture above and label it electron drift

Overall Direction

Electron Drift


Electric current

  • Heat is always a side effect of electric current (because of electron drift).

Overall Direction

Electron Drift


Electric current

  • A potential difference (V) between two points creates an electric field

  • An electric field moves through a circuit setting electrons in motion


Electric current

Direct Current (DC)

  • Electrons move in one direction

    • The positive terminal provides the electrons


Electric current

Alternating Current (AC)

  • Electrons constantly change directions


Alternating current ac

Alternating Current (ac)

  • In USA, direction changes 60 times per second


Electric current

  • Conventional way to draw current

    • Current moves from the positive to negative terminal

Load

Battery

Closed Switch


Equation sheet

Equation Sheet

  • Take out your equation sheet and find todays equations

OHM’S LAW


Write these equations in your notes

Write these equations in your notes

Ohm’s Law

V=IR

P=IV


Electric current

  • What do the following variables stand for and what are their units?

    Draw this table in your notes


Electric current

  • What do the following variables stand for and what are their units?

Volts or (V)

Voltage

Amperes or (A)

Current

Ohms or (Ω)

Resistance

Watts or (W)

Power


Electric current

  • For any electronic device (load) to work there must be a current

  • Electrical Current (I): Continuous flow of electrons

Ohm’s Law

V=IR


Electric current

  • For a current you need a conductive path

  • And a voltage (potential difference)

    • More electrons in one area than another

-

+

e

Wire

e

e

e

e

e

e

e

e

e

e

e

electron

e


Electric current

e

e

e

e

e

e

e

  • What happens when there is no more potential difference (voltage)?

  • To create this difference, work must be done adding electrons by a charge pump

e

e

e

e

e

e

e

e

e

e

e

e

electron

e


Charge pumps sources of pumping electrons

e

e

e

e

e

e

e

Charge Pumps (sources of pumping electrons):

  • Photocell - light energy into electrical

    Ex: solar cell

  • Battery - chemical energy into electrical

  • Generator – mechanical energy (motion) into electrical

    Example: turbine


Electric current

  • Electric energy (from charge pumps) can be converted into:

  • Heat

  • Light

  • Sound


Electric current

Another factor effecting current

  • Resistance (R) – an opposition to the passage of electrons

  • If the wire was thinner would the resistance go up or down?

Ohm’s Law

V=IR

e

Wire

e

e

e

e

e

e

e

e

e

e

e

electron

e


Electric current

Another factor effecting current

  • Resistance (R) – an opposition to the passage of electrons

  • If the wire was shorter would the resistance go up or down?

Ohm’s Law

V=IR

e

e

e

e

e

e

e

e

e

e

e

Wire

e

electron

e


Factors affecting resistance of a wire

Factors affecting resistance of a wire

  • Thickness: the thicker the wire the lower the resistance

  • Length: The shorter the wire the lower the resistance

  • Type of metal: gold, silver, and copper have the lowest resistance

  • Temperature: The lower the temperature, the lower the resistance


Questions

Questions

V=IR

  • Rearrange this equation for current (I)

  • How is voltage (V) and current (I) related?

  • How is Resistance (R) and current (I) related?

Directly (if V increases, I increases)

Inversely (if R increases , I decreases)


Electric current

P=IV

Power (P) is the rate of energy use (change in energy)

Power is also related to current and voltage by this equation.


Problem set 1

Problem Set 1

  • What is the resistance of an electric frying pan that draws 12 amps of current when connected to a 110v circuit?

  • How much current is drawn by a 23Ω lamp when a voltage of 12v is applied?

  • What is the voltage of a battery if it produces a current of 0.75 amps in a 12Ω resistor?


Problem set 11

Problem Set 1

  • What is the resistance of an electric frying pan that draws 12 amps of current when connected to a 110v circuit?


Problem set 12

Problem Set 1

2. How much current is drawn by a 23Ω lamp when a voltage of 12v is applied?


Problem set 13

Problem Set 1

3. What is the voltage of a battery if it produces a current of 0.75 amps in a 12Ω resistor?


Effects of current on the body

Effects of current on the body

  • 0.001a (1 ma) – barely felt

  • 0.005a (5 ma) – painful

  • 0.010a (10 ma) – muscles contract

  • 0.015a (15 ma) – loss of muscle control

  • 0.100a (100 ma) – can be fatal if the current goes through the heart


Safety notes

Safety Notes

  • Electricians often put their hand in their pocket to avoid current going through heart (just in case)

  • Electricians touch a wire they think is not live with the back of their hand so they are not stuck clinching the wire if they were mistakenly wrong


Modified equations

Modified Equations

V=IRP=IV

Add to your equation sheet:

P = I2R

P=IV

IR substituted for V

V=IR


Modified equations1

Modified Equations

V=IRP=IV

Add to your equation sheet:

P = I2R

P=IV

substituted for I


Problem set 2

Problem Set 2

  • An appliance draws 13a when connected to a 110 v circuit.

    a) what is the power of the appliance

    b) What is its resistance

    2. What is the power of a light bulb that has a resistance of 190 ohms in a 120 v circuit?


Problem set 21

Problem Set 2

  • An appliance draws 13a when connected to a 110 v circuit.

    a) what is the power of the appliance

    b) What is its resistance


Problem set 22

Problem Set 2

2. What is the power of a light bulb that has a resistance of 190 ohms in a 120 v circuit?


Electric current

“Power” companies sell us energy. The unit they use for energy is the kilowatt hour.

Physics challenge:

What is the smallest denomination coin you could use to pay for the energy used by a 60w bulb burning for 8 hours? (at a cost 16.0412 cents per kilowatt hour)

Add to your equation sheet


Electric current

“Power” companies sell us energy. The unit they use for energy is the kilowatt hour.

Physics challenge:

What is the smallest denomination coin you could use to pay for the energy used by a 60w bulb burning for 8 hours? (at a cost 16.0412 cents per kilowatt hour)

Start by converting 60W to kW

60W

1 kW

= 0.060 kW

1000 W


Electric current

“Power” companies sell us energy. The unit they use for energy is the kilowatt hour.

Physics challenge:

What is the smallest denomination coin you could use to pay for the energy used by a 60w bulb burning for 8 hours? (at a cost 16.0412 cents per kilowatt hour)

kW


Ws packet

WS PACKET

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