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AS Physics PiA Spec > Sensing > Flashcards

Sensing Flashcards

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1
Q

Current

A

Rate of flow of charged particles. Conserved across the circuit –> current flowing into a junction = current flowing out of a junction: I(total)=I1+I2+I3

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2
Q

Current=

A

Q/t (Q is the charge in coulombs)

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3
Q

1 coulomb

A

the amount of charge that passes in 1 second when the current is 1 ampere

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4
Q

Potential difference

A

Energy per unit charge. To make a charge flow, work must be done. Potential difference is the energy converted per unit charge moved

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5
Q

Potential difference, V=

A

E/Q

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6
Q

1 volt

A

Potential difference is 1 volt when 1 joule of energy is used to move 1 coulomb of charge: 1V = 1JC^-1

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7
Q

Resistance

A

How much current flows across a component when a potential difference is applied to it. Comes from electrons colliding with atoms and losing energy

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8
Q

1 ohm

A

A component has resistance 1 ohm when a potential difference of 1 volt results in a current of 1 amp

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9
Q

Resistance, R=

A

V/I

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10
Q

I/V graphs

A

The gradient of current/p.d. graphs shows the resistance - be careful!!! if current is on the y axis, and voltage on the x, the gradient is I/V which is the conductance –> shallow gradient is a high resistance

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11
Q

Ohmic conductors

A

Resistance is constant for all currents and voltages - the conductors obey Ohm’s law

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12
Q

Ohm’s law

A

Provided the temperature is constant, the current through an ohmic conductor is directly proportional to the potential difference across it.

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13
Q

I/V graph of a filament lamp

A

Has an s-shaped curve - starts steep, then gets shallower. This is because as the filament gets hotter, the resistance increases.

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14
Q

Resistance of a thermistor

A

Depends on temperature. For most thermistors, the resistance decreases as the temperature increases - I/V graph starts shallow and gets steeper. As thermistor gets warmer, more electrons are freed to become charge carriers.

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15
Q

Sensitivity

A

Change in dependent variable/Change in independent variable –> change in voltage/change in environment

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16
Q

Series circuits

A
  • current is constant across all points (no junctions)

- e.m.f. split between components: E=V1+V2+V3+etc => IR(total)=IR1+IR2+IR3+etc (as V=IR) => R(total)=R1+R2+R3+etc

17
Q

Parallel circuits

A
  • current is split at each juction: I(total)=I1+I2+I3+etc

- same p.d. across each loop => V/R(total)=V/R1+V/R2+V/R3+etc => 1/R(total)-1/R1+1/R2+1/R3+etc => G(total)=G1+G2+G3+etc

18
Q

Internal resistance

A

Chemical energy is used to make electrons move in batteries. When they move, they collide with atoms, so the battery has resistance.

19
Q

E.M.F

A

Electromotive force - NOT A FORCE!!! The amount of electrical energy produced for each coulomb of charge, measured in volts

20
Q

Terminal potential difference

A

The p.d. across the load resistance (R). The energy transferred when one coulomb of charge flows through the load resistance.

21
Q

E.M.F and internal resistance equations

A

e=V+v ; e=I(R+r) ; V=e-v ; V=e-Ir (where e is e.m.f, V is terminal p.d, v is lost volts across battery, I is current, R is load resistance and r is internal resistance)

22
Q

Why low internal resistances are important (and exception)

A

In a car battery, a high current is delivered, so a low internal resistance is required.
High voltage power supplies are the exception. HT and EH (high tension and extremely HT) have very high internal resistances, so if they’re short-circuited, only a small current can flow - much safer.

23
Q

Power and power dissipation

A

Rate that a component converts electrical energy into other types of energy, e.g. heat - power dissipation. Useful in light bulbs - makes them shine. Unhelpful in computers - have to keep them cold

24
Q

Power=

A

IV=I^2R=V^2/R

25
Q

Potential divider

A

A circuit with a voltage source and some resistors in series. The potential of the voltage source (e.g. power supply) is divided between the resistors

26
Q

Potential divider equations

A

V(out)=(R1/(R1+R2)).V(total) ; V1/V2 = R1/R2

27
Q

Transistor

A

A kind of switch. Off when voltage across is low, on when voltage across is high

28
Q

LDR

A

High resistance in dark, low resistance in light

29
Q

NTC thermistor

A

High resistance at low temperatures, low resistance at high temperatures - OPPOSITE to a normal resistor

30
Q

Conductance, G=

A

1/R=I/V

31
Q

Energy, E=

A

Pt=VIt

AS Physics PiA Spec (3 decks)

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