Chapter 2 Sensing Flashcards
What is one way to make tiny objects out of silicon?
To deposit material on a silicon surface and then selectively cut away parts with acids and other chemical.
Explain an accurate way to make tiny objects.
To bombard the object with a beam of fast moving charged particles. It works very much like using a sand-blasting strip paint.Rapidly moving ions blast away surface atoms,knocking them out of the surface, making it possible to smooth or shape a surface right down to the atomic scale.
What is the name of the process that blast material with ions?
Ion-beam machining.
Why must a beam been in a vacuum if you want it to carry a current?
If not the ions will be scattered by colliding with gas molecules.
Give some examples of moving charged particles.
1) The beam of electrons which lights up the screen of your television set.
2) A beam of protons in a particle accelerator used to probe the nature of matter.
3) Charged particles coming from the Sun causing the Northern light.
What is the charge of one electron?
1.6 x 10^-19 C
Where does current go?
Current moves in the direction potential energy decreases.
Explain how there is potential difference formed in a dry cell.
The chemical reaction drives electrons to one pole leaving positive charge at the other. The difference in distribution of charges creates a potential difference between the poles.
Explain how there is potential difference in a storm cloud.
Strong air currents rub ice crystals against one another,separating charges. The potential difference between top and bottom of the cloud can be millions of volts.
Explain how there is potential difference in a nerve cell.
“Pumps” in the walls of the cell drive sodium ions outside the cell. This difference leads to a potential difference of about 70 mV between inside and outside.
How is potential difference formed?
By uneven distributions of charges make potential difference.
How do ions beams help make silicon more conductive?
Ions beam are used to “implant” ions in silicon to make it conduct electricity better.
What is electric current?
The rate of flow of charge.
What is power?
The rate of delivery of energy.
What is the equation relating current with a beam of ions.
I=NQ
Where N is ions arriving per second and Q is charge of the ion.
A particle accelerator delivers a million singly charged ions to a target every microsecond.What is the beam current?
0.16^-6 (micro amps)
The electron beam in a television set is given energy by travelling across a potential difference of 10KV. What is the potential difference generated by the battery?
5mA
How many electrons are there in one coulomb?
6.25x 10^18
The energy given to an electron as it goes from one terminal to the other of a battery is 2.4 x 10^-19 J. What is the potential difference generated by the battery?
1.5V
An electron given energy by travelling across a potential difference of about 20V can knock another electron out of an argon atom.What energy does it have before the collision?
3.2 x 10^-18 J
What does an electric current consist of?
Consists of moving charged particles.
How pure is silicon?
Silicon crystals with much less than one part in a billion of impurities are grown.
What is meant by when silicon is “doped”?
New layers of the material are evaporated onto the surface,protective layers are added and then cut away selectively, and chemical are used to etch shapes into the material.
Explain how current is carried in electroplating with a solution of copper sulphate.
Current is carried by positive copper ions and by negative sulphate ions. The ions move from one electrode to the other.
What does conductance measure?
The conductance G measures how well a wire,a chop component or an electroplating cell conducts.
What is the unit of conductance?
Amperes per volts, or siemens.
Why does the resistance increase when a resistor is heated?
Positive ions in the resistor vibrate causing them to more likely be in the way.
What does Ohm’s law state?
That the conductance, and resistance of a given component is constant.The same value can be used in calculations whatever the current or potential difference.
What is ohmic what is not?
Most metals are ohmic at constant temperature, ionised gases are not.
A silicon component in a chip has a conductance of 10 micro A/V what is the resistance?
10^5
A typical 60W mains light bulb carries a current of 0.25A. How much current is drawn if five such lamps are connected together in parallel?
1.25 A
A silicon strip in a microchip has a resistance of 10^4 ohms. What is the resistance of ten such strips connected in series?What is the conductance of ten such strips connected in parallel? What is this expressed as a resisitance?
1) 10^5
2) 10^-3
3) 10^3
How is current carried?
Carried in conductors by mobile charge carries which move under a potential difference.
What is Emf?
Well basically it stands for electro motive force, it is the energy the battery provides for the circuit. Emf does not count for the internal resistance.
Internal resistance + external resistance =
The emf or E
Give all the different equations for emf.
1) E=I(R+r)
2) E= IR +Ir (r=internal resistance)
3) E= V + Ir
4) E=E/Q (E/Q stands for energy per coulomb.
