Wkb Chapter 5: Circuits

Note: each item preceded by the - must be done and handed in as part of a Class Activity.

Do 5.2a

- 5.1.1a Ask and discuss

- 5.1.1b ditto

- 5.1.1c Ask Why? Does a body in mid air have to wait til some other body from above hits it before it falls to earth?

rite answer: Individual electrons do not exert net forces on each other so force must come from somewhere else.

Definition of electron current (different from "current" we'll see later) Page 169 read it!

do 5.2.1a and discuss

Heating filiment. Read bottom of page 170 about #14 & 48 bulbs.

Discuss 5.2.1 b

5.2.2 Batteries: Read paragraph 1 & 2

- Steady State: What is it?

Discuss Figure at bottom of pg 171

Difference between "static Equilibrium" and "Steady State".

- Connect batteries in series - Define and do 5.2.3a

5.2.5 Current and magnetic fields.

Make a series circuit consisting of 2 battery and 1 round bulb.

Place compass on 2 books to get it away from table.

- do 5.2.5a and b and discuss

Left hand rule - Note this is for wire on top of the compass. For the whole story, see page 190

Definition: The direction of a magnetic field is the direction the North end of the magnet points .

5.3 Amount of current

do 5.3.1

- do 5.3.1a

- 5.3.1b- Note: more current at the same voltage (whatever that is) = brighter

Thicker wire does not always equal brighter either.

5.3.2 Affect of configuration of connecting wires.

- 5.3.2a

5.3.3 - short circuit

- 5.3.3a - If you have weak batteries let me know and we'll replace them.

- 5.3.4 Length -of connecting wires- how does it affect current?

Length - of nichrome wire- how does it affect current?

5.4 - Current in different parts of the circuit.

- 5.4.1b leave the compass in one spot and move the wires to that location. Place compass on top of at least one book.

- Assign 5.4.1.c,d,e,f This is a biggie!

5.4.2 Current in series.

Do 5.4.2a -

- Do 5.4.2b,c,d,e.-Rember to keep compass stationary and move wires.

5.4.3 - Try to make a parallel circuit.

- Do 5.4.3a & b and check answers with neighbors.

- Do 5.4.3c.& d

- Do and discuss 5.4 3e.

- Assign 5.4.3.f

Assign 5.4.4 Current conservation.

- 5.5 Assign 5.5.1 a & b

Definition: electron current i = nAv - see page 187 for definition of n, A and v.

Definition : Electron mobility u see box page 188.

Know v = -uE if moving charges are negative, and v = uE if moving charges are positive.

- 5.5.3.a

- 5.5.3b i = nAv, n = answer to 5.5.3a

- 5.5.3c v = -uE, E = v/(-u) , negative indicates opposite direction of v !

- 5.5.3 d Dt = length / 4x10^-5m/s

- 5.5.3e i₁ = n A₁v₁ = nA₂v₂, E₂ = uv₂ = u(2v₁) = 2 E₁

Note: The density is the same! So, to get the same current through the smaller wire the electrons must speed up!

- 5.5.3f E₁ = E₂

A₂ = 4A₁

n₂ = 1.5 n₁

u₂ = u₁

Assign: 5.6 for homework You do not have to hand this in, but it is a real good candidate for test questions.

Homework RQ5 1-11, Hwk5-1

Hwk #2 Due Wednesday, Jan 31, 2007

RQ5 5-8 & Hwk5-1