I. Current I is _________________________________________ Ex. 22 C of charge pass a point in 4.0 seconds. Find I. I = Units: 1 coulomb/second = 1 _______________ 1 C/s = 1 ____ So the answer can be written I = ________

Amperes are ______________________ units. (m___sk) Coulombs are ______________________ units What is a coulomb written in terms of fundamental units? 1 C = Ex. How much charge passes a point if the current at the point is __________ ampere for ________seconds?

Don't forget that the amount of charge Dq passing a point can be written with units of __________________ or __________________________________ . The conversion from one unit to the other is found on pg 1 of PhysRT: 1 C = _______________________ e or 1 e = ________________________ C Ex. How many electrons pass a point in 2.5 seconds if the current at that point is 0.50 A?

To have current, you need _________________ 2 things: ___________________________ (aka ___________ source) a/ a ______: _________side or _______ potential _________side or _______ potential wire wire two _________________ The amount of ____________ depends on the metals used. b/ a battery = _______________cell: more cells  _________________ c/ a ______________ :

A voltage source V supplies ____________ to a circuit by setting up ___________________________ within the circuit. _______ pot. _______ pot. V flow of ___________ charge flow of ________ ( ) magnified wire cross section Electrons flow out of the ________________ side of V. This is equivalent to flow of ___ charge out of ___ side of V. The e-'s collide with _____________ of wire. This absorbs electrical __________________ and ______________ the wire. The speed of e-'s ______________ collisions is ____________, but the drift (________________) velocity of e- is __________ . .

Batteries supply a constant V  _____________ current charge moves in ___________________ t Generators supply a varying V  ________________ current  ______ I charge moves in _________________ t charge moves in __________________ In Regents Physics, we will mostly study _____ , but the basic ideas are also valid for ______.

- 2. A ________________ circuit Using circuit symbols: Ex: + Switch up  ___________ circuit  ________ current Close the switch  ____________ circuit  _____________  __________ flows  ______________ Can you have voltage without current? Can you have current without voltage?

Current I is measured with an _________________, which is often part of a DMM (______________________________ ). Its symbol is: In an electrical circuit, ammeters are connected __________________ . This means the circuit must be ________________ and the _______________ must be _____________ into it: Circuit _______ ammeter: Circuit _________ ammeter: circuit part 1 circuit part 1 circuit part 2 circuit part 3 circuit part 2 circuit part 3

Voltage V is measured with an _________________, which is often part of a _________. Its symbol is: In an electrical circuit, voltmeters are connected __________________ . This means the circuit is _______ opened up , but the _______________ must be connected _____________ two points in the circuit: Circuit: circuit part 1 circuit part 1 circuit part 2 circuit part 3 circuit part 2 circuit part 3

Ammeters measure the current that passes _________ a part of the circuit, in other words, the amount of ___________ each second that passes ____________ it. Voltmeters measure the ________________________ from one side of a part of the circuit to the other side. This is called the voltage _____________ the circuit part. It represents the ____________ or _____________ needed to force each ________________ of charge through. In symbols: Ideally, neither ammeter nor voltmeters ______________ ________________________________ , but in reality they do.

II. Resistance R - __________________________________ ____________________________________________________ _____________________________________________________ 1. Resistance occurs as a result of ________________ colliding with ___________________ and with the __________________________ , resulting in ____________ . This converts __________________energy to ___________. 2. R is a __________________ . It has _________________ . units of R: ___________________ It is a ______________________ unit. 3. Any factor that makes it more _________________for _______________ to move will through a material will __________________________________ of the material:

For _____________, there are four factors that affect how much resistance it has: A. __________________ R L B. __________________ R A

Higher T  atoms of the metal _________________ temperature: R T Higher T  atoms of the metal _________________  ________________________ for e-'s to move through the metal  more ____________________ D. ______________________ : Different metals have different numbers of ____________________ .  ______ electrons  ______ current  _______ resistance R # of free electrons

These 4 factors are summed up in: (rho) is called the _________________ of a material. depends on the ___________________ of a metal and is different for different _____________ . units of r: _________________ Lowest r = _______________ Highest r = _______________ Metals that have more free _____________ will have a _________ r and _________ R.

Ex. Calculate the resistance of 100 meters of copper wire that has a cross-sectional area of 3.44 x 10-6 m2. R = = =

A _________________is a device that is designed to have a definite amount of _________________. Resistors are used to 1. control _____________ flow; and 2. provide a _____________________ of a certain amount. Symbols: 1. resistor: 2. variable resistor:

Two materials that do not follow these rules for metals are _____________________ and ______________________ . Semiconductors (like ___________ and ______________ ) have ____________ resistance at higher temperatures. Here’s why: ___________ silicon (Si) is an _______________________ . It _____________ its outer e-’s with 4 other silicon atoms in a ___________________ bond, so that its own electrons _______________________ electricity. = Si atom = a ________ of shared e-s

3 4 5 C N Al Si Ge Phosphorus P and arsenic As outer e-’s 3 4 5 a t o m C N Al Si Ge Phosphorus P and arsenic As have __________ outer e- than Si. Boron B and gallium Ga If you add _________________ of P, As, B or Ga to pure Si, it creates extra charge carriers. This is called _____________ . Higher temps “free up” more of these extra charges and allows for more __________ and so less _____ . And because of the extra charge carriers, semiconductors have _________________ resistances that can be ______________ . They are now used in making almost all _______________________________ .

Superconductors: The resistance R of superconductors is _________ as long as the material is _____________________________. Because they have no _____ , electrons can travel through them __________ , and so they can carry ________ currents for _________________ without producing large amounts of ___________ . This in useful in the ___________________ ___________ and _________________________________________ Originally (around 1911), only certain ____________ were found to be superconducting. But they had to be cooled to near ___________________ using liquid helium (boiling point about _______ ) for this to happen. This is very expensive.

In _______, a new type of superconductor was discovered whose makeup is similar to ________________ . These become superconductors at higher temperatures. This makes them much more ____________________. Material metal=m ceramic=c critical temp. (K) absolute zero Zinc 0.88 Aluminum 1.19 Tin 3.72 Mercury 4.15 liquid nitrogen YBa2Cu3O7 90 TlBaCaCuO 125 room temp. 293 much ___________ to use liquid N

III. Ohm's Law Using R = rL/A, R can be found using the ____________________________of a metal wire. In a circuit, R is defined for any device as the ratio of __________________ the device to the ________________________the device: A simple circuit:

Ex. If the potential difference across a resistor is _______ and the current through it is __________, find R. units: [ ] = [ ]/[ ] =

To remember all 3 equations, use: V = ? R = V / I Solve this for I = ? To remember all 3 equations, use: units: [V] = [I][R] = [I] = [V]/[R]

Ex: What is the potential difference across a 25-W resistor when it carries a current of 3.0 A? Ex: How much energy is required to make each coulomb of charge pass through the above resistor? Ex: What is the potential difference across a wire that has no resistance?

1. Assume the connecting wires have _________________ resistance. (They usually have ________________ R than the circuit elements.) For simple devices such as _______________________ , we often replace the device with the symbol for __________________ : and assume that it has all of the ______________________. I = charge flowing _______________________________ . The charge going __________ any circuit element must _________ the charge __________ that element. Assume ____ charge flows out of the ____ side of the source. V = potential difference __________________ = ____________________________ available to do work = energy converted to _______________________ by R = energy is __________________ by passing through R = _________________________ across R = _______ if there is no resistance, e.g. in a __________

Ex: A simple circuit has 1 _______. All of the __________________ is dropped across the ___________, because it is the only element in the circuit that requires ____________ (voltage). V source R Graph the voltage drops as you follow ____________ charge from the _________ potential side of source, through the _____________ , back to the _______ side of the source. no V dropped in wire b/c V = IR = ________ V distance around the circuit

A simple circuit with ____________: ammeter – measures current passing ____________ R - Ideally, it has no ____, so no ________ across it voltmeter – measures potential difference _________ R - Ideally, it does not allow any ____ to enter it The voltmeter must be connected across _______________ sides of R to measure potential _____________. R Other ____________________ways to hook up the meters:

Remember: V ____________ I  So changing V _______________ I. Ohm’s Law: For __________________ conductors at _______________ temp., I is ___________ prop. to V. Case A: a device obeys Ohm’s Law  _____________ V I slope = ΔV/ΔI = constant so the ratio V/I = ____ is ___________ Case B: ________________ devices V I  slope = V/I = R is ________________ In the case shown, R _______________ (Traditionally, V is plotted on the ____ axis)

Ex. If R is _____________ , then I is _____________ . As R  ____, I  ____ . This is an ___________ circuit. V = R = V Ex. If R is ___________ , then I is _____________ . As R  ____, I  ____ . This is a ___________ circuit. R = V V = This situation can be _______________________________ . Body resistance can be lowered by getting __________ .

"It's _______________ that jolts, (shocks you) But it's ___________ (milliamps of current) that kills." Currents and the harm they can cause: AC tends to send heart nerves into _______________, which can be harder to fix than simply ________________________.

A__________, short for 'fusible link', is a type of overcurrent protection device. Its essential component is a __________________________________________________ ____________________ . Fuses usually are rated in _______________ . If the current exceeds the rating, the metal strip melts, and it _________ the circuit. This protects the circuit from __________________ which may damage other circuit parts or ________________ . A _______________________ is an automatically-operated electrical ______________ . Like a fuse, it is designed to protect an electrical circuit from damage caused by excess_________. Unlike a fuse, which operates once and then must be replaced, a circuit breaker ________________ once the problem that caused the excess current is fixed.

A downed power line can set up a _________ through the ground. Since the cables have _______ R, most voltage will be dropped along _________________ . If the distance between the downed line and the source is _________, there can be large _________ between 2 nearby points along the ground between your feet. ___________ or ____________!

IV. Series circuits - ____________________________________ ___________________________________________________ circuit element ___ wire wire ________ potential voltage source circuit element ___ ________ potential wire circuit element ___ wire Assume: 1. _____________________________________________________ 2. _____________________________________________________ 3. _____________________________________________________ 4. _____________________________________________________

For a circuit with 2 resistors: _______________ Conservation: V = _______________ Conservation: I = _______________ (Total) Resistance: Req = __________ Law applies to the total: V = and to each individual element: V1 = V2 =

Ex. Find all the voltages and currents in the circuit below: V1 = I1 = R1 = V2 = I2 = R2 = V = I = Req =

Form the __________ of each resistance to Req = ________ , and then multiply by the ___________ voltage V. V = 20. V 40 W R1 Req 120 W R2 Req V “divides up” ______________________________ as the R’s This is because ___________ R requires _________ energy. Series circuits are _______________________________.

Plot V vs. “distance around circuit.” back to ____ side of the battery Plot V vs. “distance around circuit.” ____ side of battery 20 V dropped across the ______ resistor 15 potential difference (V) V dropped across the ______ R at the ___ side of the battery distance around circuit ________ drop across wires because we assume ________

Important: “I is ______________ everywhere in ___________ circuit” does NOT mean that I is ___________ in _________________ circuit! I = I1 = I2 = 10. V R1= R2 = I = I1 = I2 = I3 = R1= 10. V R2= R3= I is still the _______________ in all parts of the second circuit, but it is a ________________ I than the first one!

Equivalent resistance: _________________________________ ________________________________________________________ Replacing this part of the circuit with a single _______________ resistor: Req = R1 + R2 = = 20. V 40 W 120 W …gives you this circuit: The total I = 20. V This is the ____________ as before.

All _______________ circuits can be ___________________ in this way. Req = _____ W V = 20 V V = 20 V B. Req = _____ W V = 12 V V = 12 V This can be done even if the ______________________ is not shown. C. Req = _____ W D. Req = _____ W Req results in the _____________ as the _________________ circuit.

To measure I1, the current through R1, _________________ Series Circuits __________ Hookups: Original circuit: R1 V R2 To measure I1, the current through R1, _________________ the circuit and ____________ an ________________ next to R1. V R1 R1 V R2 R2 Other possibilities: R1 V V R1 R2 R2 ___ is the same everywhere, so _________________________

To measure V1, the voltage across R1, __________disconnect the circuit. Simply connect the ______________ across R1 V R1 R2 Original circuit: V R1 R2 Other possibilities: V R1 R2 V R1 R2 Similarly, to measure the _________ voltage V or V2: V R1 R2 V R1 R2

V. Parallel circuits - ___________________________________ ___________________________________________ wire wire wire ________ potential wire circuit element ___ circuit element ___ circuit element ___ circuit element ___ voltage source ________ potential wire Assume: 1. _____________________________________________________ 2. _____________________________________________________ 3. _____________________________________________________ 4. _____________________________________________________

For a circuit with 2 resistors: _______________ Conservation: V = _______________ Conservation: I = _______________ (Total) R: 1/Req = __________ Law applies to the total: V = and to each individual element: V1 = V2 =

Ex. Find all the voltages and currents in the circuit below: V1 = I1 = R1 = V2 = I2 = R2 = V = I = Req =

To find Req without using V and I: 1 Req = R1 + R2 = = = = NOTE: In a ________________ circuit, Req is __________________ either R1 or R2.

Compare the _________ of the resistances R1/R2 to the __________ of the currents: I1/I2. R1 R2 I1 But… I2 I “divides up” ______________________________ to the R’s R1 has ______ the current b/c it has __________resistance. Parallel circuits are _______________________________.

Notice what happens if one branch is __________________ : I1= V1/R1 20. V 50 W 100 W I2= V2/R2 20. V 50 W 100 W These are ____________________ answers as before. Each branch is_______________________of the others. This is why __________________ circuits are used.

Plot V vs. “distance around circuit.” back to ____ side of the battery Plot V vs. “distance around circuit.” ____ side of battery 20 potential difference (V) ____ resistor _____ resistor at the ___ side of the battery distance around circuit ______ drop across wires because we assume _________

Important: “V is ______________ everywhere in ___________ circuit” does NOT mean that V is ___________ in ______________ circuit! V= V1= V2= 10. V R1 = R2= V = V1 = V2 = R1 = 20. V R2= V is the _______________ across all parts of the second circuit, but it is a ________________ V than the first one!

Equivalent resistance: _________________________________ ________________________________________________________ Replacing this part of the circuit with a single _______________ resistor: Req = 1/(1/R1 + 1/R2) = …gives you this circuit: The total I = 20. V This is the ____________ as before.

All _______________ circuits can be ___________________ in this way. V = 3.0 V V = 3.0 V Req = ____W This can be done even if the ______________________ is not shown. B. Req = _____ W C. Req = _____ W Req results in the _____________ as the _________________ circuit.

Alternative ways to draw parallel circuits: The circuit at left can also be drawn: V R1 R2 V or: or: V V NOTE: The diagram below is _________________________ because there is ________________ __________ for the current. V

What is the equivalent resistance between points A Ex 1. Draw two 10-W resistors in parallel between points A and B. Ex 2. Draw three 60-W resistors in parallel between points A and B. A A B B What is the equivalent resistance between points A and B in each of the examples above? (Hint: For identical parallel resistors, divide 1 R by the ___________ of resistors.) Ex 1: Divide _______ by ____  Req = __________ Ex 2: Divide _______ by ____  Req = __________

A. To measure, V1, the voltage across R1, connect the Parallel Circuit __________ Hookups: Original circuit: V R1 R2 A. To measure, V1, the voltage across R1, connect the ______________ across R1. To measure I1, the current through R1, _________________ the circuit and _____________ an ________________ next to R1 R2 V ____ = where the ammeter could also be placed.

B. To measure the voltage _____________ and the current __________ resistor R2: V R1 ___ = optional ammeter position C. To measure the _________ voltage and current : R1 R2 ___ = optional ammeter position

In an ideal parallel circuit, all of the ______________ are equal, so placing the ________________ across any element gives ___________________________ . R2 V R1 In reality, each voltage will _______________________ . This is because the wires have a small amount of ______ , and so by Ohm's law: __________ , there is a small amount of _________________ dropped along each wire.

VI. Electrical Power P is the _________ at which electrical _____________________________ light, heat, mechanical, etc, energy or vice versa. P is a _____________ P The units of P are watts, W ( _____________ ) 1 watt = 1 W = = Since W = , you can write: Electrical work: W =

Ex. At what rate is electrical energy converted to heat and light in a 75 W bulb? Ex: A 55-W toaster oven is used for 25 seconds. How much electrical energy is converted to heat?

Ex. A 12-W resistor carries a current of 3.0 A for 5.0 s. a/ At what rate does the resistor convert energy? b/ How much energy does the resistor convert in the 5.0 s?

Ex: How much power is developed in the circuit at right? Given: At what rate is energy converted to heat? How much energy is converted in one minute? Ex. What quantity does P “·” represent?

Ex. R1 V V R1 R2 R2 Power of resistor R1: P1 = Power of resistor R2: P2 = Total power: P = or sum up the powers: P = All of these equations work ___________________________ .

Ex: Find the power in each resistor and the total power. V1 = I1 = R1 = P1 = V2 = I2= R2 = P2 = V = I= R = P =

Ex: Find the power in each resistor and the total power. V1 = I1 = R1 = P1 = V2 = I2= R2 = P2 = V = I= R = P =

Notice both circuits above have ____________ V, R1 and R2. Which of the two circuits would drain a battery faster? The ____________ circuit has a ______________ Req. This means it will have ____________ I. Because P = ______ and both circuits have the _____ , the _____________ circuit will develop more power. Which resistor develops more power in the series circuit? ___ b/c both have same ___ but it has more ____________ Which develops more power in the parallel circuit? ___ b/c both have same ___ but it has more ____________

__________________ passed ___________ through a wire that was submerged in __________ and found that the amount of ________ produced was proportional to ____ and _____. This is called_________ or _____ heating. Less ___ means ______________ electrical energy is converted to _______. Because P = ____ , the current can be reduced if ____ is increased. For this reason, power is transmitted at high _____________ . At your house: _________ Power plant: ~_____ The power is transmitted at _____________ A substation cuts the V to __________