in order to have an electrical potential difference (aka voltage) that drives  current in an electric circuit, we need a battery or an electric generator ,in this case the battery is a source of ______

electromotive force( emf)

(note this is not really a force measured in Newtons, just a bad name).

describe the electromotive force( emf) of a batery or a electric generator

(aka a source that can generate electrical energy)

 the potential difference btwn the terminals of the source, where no current flows to an external circuit.

unit: volts

 true or false :is a battery a source of constant current?

if false make it true

true or false :is a battery a source of constant voltage?

if false make it true

sort of;

a  battery is a source of constant voltage, but NOT  perfectly constant

battery has a small internal resistance, which reduces the actual voltage from the ideal emf.

the voltage gained by  the battery with respect to terminals in the battery ( ex A & B)

has to equal the sum of all the voltage drops due to the prescense of resistors in the circuit 

there is an internal drop in voltage equal to Ir

I= current

r= internal resistance

(aka this is theACTUAL terminal voltage)

when 2 or more resistors are connected end to end in a series

1.the total voltage is equal to?

2.the total (equivalent)resistance is equal to ?

1. sum of the voltages across each resistor

(V _total= V1+V2+V3)

=

recall ohm's law V=IR

=

 IR1+IR2+IR3

2.Req= R1 +R2+ R3

 for Resistors in Series:

The current through each resistor is ______  (equal, less, more), while the voltage depends on the _______.

The sum of the voltage 'drops'across the resistors as you go across the all the resistors in the circuit euqals the _____.

1.the same

2. resistance

3. battery voltage

for Resistors in Series:

what occurs when you add more resistance to thre circuit?

the current through the circuit will decrease.

1.what is the current of a 12 V battery if it is connected to a 4Ω resitor?

 2.also calc for 3 -4Ω resitors in a series?

1. V= IR

I= V/R

I=12/4Ω

I= 3A

2. Find total R:

3 x 4Ω = 12Ω

I= 12/12Ω

I = 1 A

 for a series of resistors that have parallel connection

what happens the current?

what happens to the voltage across each resistor

1.the current is split into seperate paths

 2.the voltage across each resistor is the same

explain the difference btwn resistors that are connected

 parallel  vs series

Parallel: how a house, buliding is wired

, if you disconnect one device the other devices are not interupted.

Series: if one device is disconnected, current is stopped to the others.

1/R_{eq =} 1/4Ω + 1/4Ω

= 2/ 4Ω

= 1/2Ω

so Req= 2

(u flipped 1/2 to 2/1)

for resistors connected in a parallel circuit the net resistance is less  than the resitance than a SINGLE resistor 

b/c the parallel arrangemnt allows the current additional paths to follow.

whenSome circuits

cannot be broken down into series & parallel connections

The sum of currents entering a junction

=

 the sum of the currents leaving it.

Kirchhoff’s Rules:

what is the loop rule?

 only if the voltages of the emfs are the same.

T or F: EMFs in a parallel arrangement is used to increase voltage

whether true or false , explain

False, a parallel arrangement are used to SAVE energy when large currents are needed.

↓

(how they save energy)each of the cells in parallel produce only a fraction of the current.

↓

so the energy loss due to internal resistance would less LESS compared to a single EMF.

(battery will go dead less quickly)

 For Circuits Containing Capacitors in Parallel

what is the formula for the total capacitance? (ex you have 3 capacitors)

Q= C eq V= C₁ V+ C₂ V+C₃ V

(recall voltages are equal for all the capacitors)

 or

C eq = C₁ + C₂ +C₃ 

* recall Q= CV

Q=charge

C=capacitance

V= voltage

 so its saying the total capitance it just the sum of the capitances

(not plugging into the formula which is V=Q/C).

is to increase the capitance

 b/c we are increasing the area of the plates where charge can accumulate

 recall Q=CV

V=Q/C1+ Q/C2+ Q/C3

=

Q( 1/C1 + 1/C2+ 1/C3)

1/Ceq= 1/C1 + 1/C2 + 1/C3

just flip it b/c this is the reciporcal

(e.g 1/2 = 2/1=2)

 b/c the current in a circuit passes through the ammeter; the ammeter should have  _____(high/low) resistance so as not to affect the current.

An ohmmeter measures resistance; it requires ______

1.resistance

2.a battery to provide a current

*If the meter has too much or (in this case) too little resistance, it can affect the measurement.

formula for resistance

R