Current and Simple Circuits

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# Current and Simple Circuits - PowerPoint PPT Presentation

Current and Simple Circuits. 1. Current 2. Conductivity Model 3. Current and Current Density. Reading Question. What quantity is represented by the symbol J ?. 1. Resistivity 2. Conductivity 3. Current density 4. Complex impedance 5. Johnston’s constant. Reading Question.

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### Current and SimpleCircuits

1. Current

2. Conductivity Model

3. Current and Current Density

What quantity is represented by the symbol J ?

1. Resistivity

2. Conductivity

3. Current density

4. Complex impedance

5. Johnston’s constant

What quantity is represented by the symbol J ?

1. Resistivity

2. Conductivity

3. Current density

4. Complex impedance

5. Johnston’s constant

The electron drift speed in a typical current-carrying wire is

1. extremely slow (≈10–4 m/s).

2. moderate (≈ 1 m/s).

3. very fast (≈104 m/s).

4. Could be any of 1, 2, or 3.

5. No numerical values were provided.

The electron drift speed in a typical current-carrying wire is

1. extremely slow (≈10–4 m/s).

2. moderate (≈ 1 m/s).

3. very fast (≈104 m/s).

4. Could be any of 1, 2, or 3.

5. No numerical values were provided.

All other things being equal, current will be larger in a wire that has a larger value of

1. conductivity.

2. resistivity.

3. the coefficient of current.

4. net charge.

5. potential.

All other things being equal, current will be larger in a wire that has a larger value of

1. conductivity.

2. resistivity.

3. the coefficient of current.

4. net charge.

5. potential.

Current and Simple Circuits

Current

How can you show that a current is a flow of charge?

Current and Simple Circuits

Current

How can you tell if a current is flowing in a wire.

Knight has

• Instantaneous current
• This current is also given by
• What does n, e and A represent?
Current and Simple Circuits

Current

• How do we define instantaneous current? Write the equation and then define current in words.
Current and Simple Circuits

Model of Conduction

• Explain drift velocity vd.

The charge carriers collide with impurities and phonons as the travel through the material to produce a current. The average velocity in the current direction is the drift velocity.

vd

Average time between

here and here.

Average distance between

here and here.

Current and Simple Circuits

Model of Conduction

• In your group discuss electrical conduction in metals. Discuss terms like drift velocity, collision time, and mean free path.
• Write a definition here.

Collision time is the time

between collisions.

Mean free path is the

average distance between

collisions

Current and Simple Circuits

Resistivity

• Table 28.2 in your text lists a number of materials with their resistivity and conductivity. What metallic conductor has the largest conductivity?
Student Workbook

Can you think of another?

I could not!

Student Workbook

Can you think of another?

I could not!

Class Questions

These four wires are made of the same metal. Rank in order, from largest to smallest, the electron currents ia to id.

1. id > ia > ib > ic

2. ib = id > ia = ic

3. ic > ia = ib > id

4. ib = ic > ia = id

5. ic > ib > ia > id

Class Questions

These four wires are made of the same metal. Rank in order, from largest to smallest, the electron currents ia to id.

1. id > ia > ib > ic

2. ib = id > ia = ic

3. ic > ia = ib > id

4. ib = ic > ia = id

5. ic > ib > ia > id

Class Questions

Rank in order, from largest to smallest, the current densities Ja to Jd in these four wires.

1. Jb = Jd > Ja > Jc

2. Jb > Ja > Jc > Jd

3. Jb > Ja = Jd > Jc

4. Jc > Jb > Ja > Jd

5. Jc > Jb > Ja = Jd

Class Questions

Rank in order, from largest to smallest, the current densities Ja to Jd in these four wires.

1. Jb = Jd > Ja > Jc

2. Jb > Ja > Jc > Jd

3. Jb > Ja = Jd > Jc

4. Jc > Jb > Ja > Jd

5. Jc > Jb > Ja = Jd

Current and Simple Circuits

Battery

Look at old

PP lecture

Current and Simple Circuits

Current flows from higher potential (+) to lower potential (-).

Battery

or emf

Resistor

I

For a current to flow you have to have a complete circuit.

Current and Simple Circuits

What about current flow when there are two paths?

Current splits at the junction or node.

Current and Simple Circuits

Here is our simple circuit again with just an emf and resistor. Now we would like to look at the voltage difference around the circuit.

Current and Simple Circuits

Here is our simple circuit again with just an emf and resistor. Now we would like to look at the voltage difference around the circuit.

A semiconductor is a material that has conductive

between a conductor and an insulator. The conductivity

is very strongly temperature dependent.

Si

Doped with Al is P type

Doped with P is N type

Current and Simple Circuits

Semiconductor Material

Current and Simple Circuits
• Field Effect Transistor

Superconducting elements

Current and Simple Circuits
• Superconductor

A superconductor is a material that has zero resistance below a critical temperature TC

TC

Current and Simple Circuits
• Superconductor

Perfect Conductor

Meissner Effect

- 4800 F

Current and Simple Circuits

A Biological example: Ionic current across a cell membrane.