Lecture 27Lecture 27

Electricity & ApplicationsElectricity & Applications

toto

MusicMusic

Probe the Class OPProbe the Class OP

Last time we looked at some Last time we looked at some electrical circuitselectrical circuits

We identified charge.We identified charge. Current is the charge per unit time that Current is the charge per unit time that

passes through a point of a “circuit”.passes through a point of a “circuit”. The current increases with the voltage The current increases with the voltage

across a “resistor” such as a light bulb.across a “resistor” such as a light bulb.– The brightness of the bulb depends on the The brightness of the bulb depends on the

current through it.current through it. We used OHM’S LAWWe used OHM’S LAW

– Voltage (volts) = Current (Amps) x Resistance Voltage (volts) = Current (Amps) x Resistance (ohms)(ohms)

Mr. Ohm’s LegislationMr. Ohm’s Legislation

I

VR

R

VI

IRV

200 Watts 60 Watts

POWERPOWER

Let’s move a charge Let’s move a charge q from one side to q from one side to the other in a time the other in a time “t”.“t”.

V=work/chargeV=work/charge Work we do = qVWork we do = qV Power = qV/tPower = qV/t i=q/ti=q/t Power = iV Power = iV

V

i

Resistance = R

More on Power through a More on Power through a ResistorResistor

R

VV

R

VIVP

also

RIIRIIVP

IVTime

WorkPower

2

2)(

R is fixed, so

more power = morecurrent = more light!

The USA at night.

LOTS OF BULBS!

Will the bulb in (a) be brighter, dimmer, or the same brightness as any one bulb in (b)?

Which bulb in (b) is the brightest?

What would happen if one of the bulbs in (b) burned out?

A MagnetA Magnet

S NS N +Q

OP Survey

Magnets - SummaryMagnets - Summary

Magnets Do NOT attract Magnets Do NOT attract chages.chages.

Magnets have N and S polesMagnets have N and S polesLike poles repelLike poles repelUnlike poles attractUnlike poles attract

Other ObservationsOther Observations

A magnet moving into a coil produces A magnet moving into a coil produces an electric current (and voltage!).an electric current (and voltage!).

There is a “magnetic field” around a There is a “magnetic field” around a wire.wire.

A loop of wire acts like a small A loop of wire acts like a small magnet.magnet.

A wire moving near a magnet A wire moving near a magnet will have a current generated will have a current generated in it.in it.

The Dynamic MicrophoneThe Dynamic Microphone

V

The VOLTAGE is passed on to the next part of the circuit

Dynamic MicrophonesDynamic Microphones

The Voltage is the audio signal. Dynamic microphones are extremely

rugged and may be the most widely used microphones in television production.

They are relatively in expensive (for professional‑quality microphones) and usually have good frequency response.

They tend to be somewhat less sensitive to high‑frequency sounds than are condenser microphones

They Come in all Colors too!They Come in all Colors too!

Condenser MicrophonesCondenser Microphones

Add a Resistor to get the Voltage

ElectretsElectrets Both plates are electrically charged, and

sound hitting the faceplate causes a change in voltage.

Electret condensers are a popular type of condenser microphone.

Electrets are manufactured with a permanent electric charge in the capaci tor and therefore require the use of only a very small battery as a power source to boost the output signal of the microphone to a usable level.

As a result, electret condensers tend to be significantly smaller than other con denser microphones.

Different strokes …Different strokes …

Bigger is Lower!Bigger is Lower!Frequency ResponseFrequency Response

DirectionalityDirectionality

““Stereo” MicrophoneStereo” Microphone

The Process We Are Looking The Process We Are Looking AtAt

Sound ProductionMicrophoneconversion

to electrical signal

Amplify the VoltageLoud Speakerof some type

LISTENER

AmplifierAmplifier

IN

out

SLIGHT TURN

The Simple Transistor AmplifierThe Simple Transistor Amplifier(Bipolar)(Bipolar)

The VoltagesThe Voltages

NOTE SCALE DIFFERENCES

Don’t push an amplifier too Don’t push an amplifier too hardhard

The Speakers … all kindsThe Speakers … all kinds

Exploded ViewExploded View

CommentsComments

A speakers maximum response is at A speakers maximum response is at resonance.resonance.

The heavier the structure, the lower The heavier the structure, the lower the resonance frequency.the resonance frequency.– In order to cover the entire audio range In order to cover the entire audio range

we need multiple speakers.we need multiple speakers. Woofer/Sub-Woofer for low frequencyWoofer/Sub-Woofer for low frequency ““Tweeter” for high frequencyTweeter” for high frequency Mid range speakers as well.Mid range speakers as well.

Frequency RangesFrequency Rangesfor different types of speakers.for different types of speakers.

Another Music ApplicationAnother Music Application

Multiple Sources of SoundMultiple Sources of Sound

The StringsThe Strings

The “Package”The “Package”

The InstrumentA Combination

Amplifierand

Speaker

Next Step (If We Get To It)Next Step (If We Get To It)

The “new The “new ElectronicsElectronics

The Digital WorldThe Digital World CompressionCompression The CD to the IPODThe CD to the IPOD