Samenvatting
Samenvatting BMAT natuurkunde (geneeskunde selectie, 2021) in het engels
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- BMAT Natuurkunde In Het Engels
Samenvatting van BMAT natuurkunde (sectie 2).
[Meer zien]Voorbeeld 4 van de 41 pagina's
Voorbeeld 4 van de 41 pagina's
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Voorbeeld van de inhoud
P1 - ElectricityCharge (Q) is measured in Coulombs (C). One electron has a charge of 1.6x10-19 C. 1 Coulomb is
defined as the amount of charge that passes in 1 second when the current is 1 Ampere (though you
probably don’t need to know this).
Current (I) is the rate of flow of charge, and is measured in Amperes (A). A current of 1A means that
Q
1 coulomb of charge flows past that point every second (hence the term “rate”). So I =
t
Current is measured with Ammeters which are placed in series within a circuit – hence, they measure
current at a specific point.
Potential Difference (Voltage, V) is measured in volts (V), and is the work done per unit charge. 1V
means that 1 Joule of work is done in pushing 1 coulomb of charge through a particular
Energy
area/component, so U =
Q(charge)
Voltmeters are placed in parallel and have infinite resistance, so they measure current between 2
points in a circuit. We’ll come back to the point about infinite resistance when discussing series and
parallel circuits, so don't worry about it just now.
Resistance (R) is difficult to define, but is measured in Ohms (Ω). Some people call it the ratio of
voltage to current, which is a pretty obvious definition when you consider Ohm’s Law, which we all
U
know: R=
I
Power (P) is measured in watts (W) and is defined as the rate of transfer of energy. 1W is the
transfer of 1 Joule of energy per second.
There are two basic formulae for power that you need to know:
E
P= P=I ×U
t
(E = energy in Joules, I = current, t = time, V = voltage)
Energy transfer = P x t = I × U × t
,Electrical circuit:
Series - When components are connected one after the other, along the same loop of the
circuit, they are connected in series.
Parallel - When components are connected along separate loops of the circuit, they are
connected in parallel.
Series: Voltage:
Utot = U1 + U2 + U3 …..
Itot = I1 = I2 = I3
Rtot = R1 + R2 + R3
current:
Parallel:
Utot = U1 = U2 = U3 ….
,Itot = I1 + I2 + I3
1 1 1 1
= + + (so the total resistance is lower than any individual resistance)
Rtot R1 R2 R 3
Alternating Current (AC) is a type of
electrical current, in which the direction of
the flow of electrons switches back and forth
at regular intervals or cycles.
Direct current (DC) is electrical current which
flows consistently in one direction. The
current that flows in a flashlight or another
appliance running on batteries is direct
current.
NTC thermistors: (NTC: Negative temperature coefficient) Thermistors are used as temperature
sensors, for example, in fire alarms. In the most common type of thermistor,
the resistance decreases as the temperature increases:
at low temperatures, the resistance of a thermistor is high and little current can flow through
them
at high temperatures, the resistance of a thermistor is low and more current can flow
through them
LDR’s: LDRs (light-dependent resistors) are used to detect light levels, for example, in automatic
security lights. Their resistance decreases as the light intensity increases:
in the dark and at low light levels, the resistance of an LDR is high and little current can flow
through it
Ideal diodes: Diodes are electronic components which can be used to regulate the potential
difference in circuits and to make logic gates. A diode has a very high resistance in one direction. This
means that current can only flow in the other direction.
Fixed resistor:
, For a fixed resistor, the potential
difference is directly proportional to
the current. Doubling the amount of
energy into the resistor results in a
current twice as big through the
resistor. This relationship is
called Ohm's Law and is true
because the resistance of the
resistor is fixed and does not
change.
Filament Bulb:
In a filament bulb, the current does not increase
as fast as the potential difference (voltage).
Doubling the amount of energy does not cause a
current twice as big.
The more energy that is put into the bulb, the
harder it is for the current to flow - the resistance
of the bulb increases. As the potential difference
increases, so does the temperature of the thin
wire inside the bulb, the filament. The
increased vibrations of the ions in the filament
because of the increased temperature make it
harder for the electrons to get past.
Conductors: materials that let electricity pass through them easily, like cupper, iron and steel
Insulators: materials do not allow electricity to pass through them, like plastic, wood and glass
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