Electric Current

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# Electric Current - PowerPoint PPT Presentation

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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Presentation Transcript

Section 1-3

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

Open Switch

Conductor

Closed Switch

+

Battery

-

A light is an example of a load

Fuse

Basic Circuit

Resistor

Open Switch

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

Closed Switch

Conductor

+

Battery

-

Fuse

Resistor

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

Lights on Lights off

An open circuit is off

Lights on Lights off

A closed circuit is on

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

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

Overall Direction

Electron Drift

A potential difference (V) between two points creates an electric field
• An electric field moves through a circuit setting electrons in motion
Direct Current (DC)
• Electrons move in one direction
• The positive terminal provides the electrons
Alternating Current (AC)
• Electrons constantly change directions
Alternating Current (ac)
• In USA, direction changes 60 times per second
Conventional way to draw current
• Current moves from the positive to negative terminal

Battery

Closed Switch

Equation Sheet
• Take out your equation sheet and find todays equations

OHM’S LAW

Draw this table in your notes

Volts or (V)

Voltage

Amperes or (A)

Current

Ohms or (Ω)

Resistance

Watts or (W)

Power

• Electrical Current (I): Continuous flow of electrons

Ohm’s Law

V=IR

For a current you need a conductive path
• And a voltage (potential difference)
• More electrons in one area than another

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Wire

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electron

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• What happens when there is no more potential difference (voltage)?
• To create this difference, work must be done adding electrons by a charge pump

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electron

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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

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

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electron

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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

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Wire

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electron

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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

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)

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
• 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 1
• What is the resistance of an electric frying pan that draws 12 amps of current when connected to a 110v circuit?
Problem Set 1

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

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
• 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
• 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

V=IR P=IV

P = I2R

P=IV

IR substituted for V

V=IR

Modified Equations

V=IR P=IV

P = I2R

P=IV

substituted for I

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 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 2

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

“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)

“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

“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
• Do Section 2-3 Ohm’s Law and Power