Chapter 2 Sensing

Question 1

What is one way to make tiny objects out of silicon?

Answer 1

To deposit material on a silicon surface and then selectively cut away parts with acids and other chemical.

Question 2

Explain an accurate way to make tiny objects.

Answer 2

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.

Question 3

What is the name of the process that blast material with ions?

Answer 3

Ion-beam machining.

Question 4

Why must a beam been in a vacuum if you want it to carry a current?

Answer 4

If not the ions will be scattered by colliding with gas molecules.

Question 5

Give some examples of moving charged particles.

Answer 5

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.

Question 6

What is the charge of one electron?

Answer 6

1.6 x 10^-19 C

Question 7

Where does current go?

Answer 7

Current moves in the direction potential energy decreases.

Question 8

Explain how there is potential difference formed in a dry cell.

Answer 8

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.

Question 9

Explain how there is potential difference in a storm cloud.

Answer 9

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.

Question 10

Explain how there is potential difference in a nerve cell.

Answer 10

“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.

Question 11

How is potential difference formed?

Answer 11

By uneven distributions of charges make potential difference.

Question 12

How do ions beams help make silicon more conductive?

Answer 12

Ions beam are used to “implant” ions in silicon to make it conduct electricity better.

Question 13

What is electric current?

Answer 13

The rate of flow of charge.

Question 14

What is power?

Answer 14

The rate of delivery of energy.

Question 15

What is the equation relating current with a beam of ions.

Answer 15

I=NQ

Where N is ions arriving per second and Q is charge of the ion.

Question 16

A particle accelerator delivers a million singly charged ions to a target every microsecond.What is the beam current?

Answer 16

0.16^-6 (micro amps)

Question 17

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?

Answer 17

5mA

Question 18

How many electrons are there in one coulomb?

Answer 18

6.25x 10^18

Question 19

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?

Answer 19

1.5V

Question 20

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?

Answer 20

3.2 x 10^-18 J

Question 21

What does an electric current consist of?

Answer 21

Consists of moving charged particles.

Question 22

How pure is silicon?

Answer 22

Silicon crystals with much less than one part in a billion of impurities are grown.

Question 23

What is meant by when silicon is “doped”?

Answer 23

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.

Question 24

Explain how current is carried in electroplating with a solution of copper sulphate.

Answer 24

Current is carried by positive copper ions and by negative sulphate ions. The ions move from one electrode to the other.

Question 25

What does conductance measure?

Answer 25

The conductance G measures how well a wire,a chop component or an electroplating cell conducts.

Question 26

What is the unit of conductance?

Answer 26

Amperes per volts, or siemens.

Question 27

Why does the resistance increase when a resistor is heated?

Answer 27

Positive ions in the resistor vibrate causing them to more likely be in the way.

Question 28

What does Ohm’s law state?

Answer 28

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.

Question 29

What is ohmic what is not?

Answer 29

Most metals are ohmic at constant temperature, ionised gases are not.

Question 30

A silicon component in a chip has a conductance of 10 micro A/V what is the resistance?

Answer 30

10^5

Question 31

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?

Answer 31

1.25 A

Question 32

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?

Answer 32

1) 10^5
2) 10^-3
3) 10^3

Question 33

How is current carried?

Answer 33

Carried in conductors by mobile charge carries which move under a potential difference.

Question 34

What is Emf?

Answer 34

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.

Question 35

Internal resistance + external resistance =

Answer 35

The emf or E

Question 36

Give all the different equations for emf.

Answer 36

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.