Science chapter 13 Flashcards
An electrical system comprises of
-connecting wires
-dry cell, one
-dry cells, two in
series
-switch (open)
-switch (closed)
-light bulb
The SI unit of current is the
ampere (A). One ampere of
current means that one unit charge flows in one second.
We measure current using an
ammeter, + to +, - to -
What is an electric current
An electric current is the rate of flow of electric charge.
How does conventional current flow
current flows
from the positive terminal of a battery to
the negative terminal.
How does the electron current flow
it flows from the negative to the
positive terminal.
An electric current can flow only
when there is a
potential difference
An ammeter must be connected in
series in a
circuit.
What is the potential difference between any two points
it is the amount of energy needed to move one unit of electric charge from one point to another
The SI unit of potential difference is
Volt (V)
The more energy needed to move a charge
between two points in a circuit, the greater the
potential difference between the two points.
the greater the
potential difference between the two points.
We measure potential difference using a
voltmeter
The voltmeter must be connected in
parallel
What is the resistance of a component is the ratio of
the potential difference across it to the current
flowing through it.
It is the ratio of
the potential difference across it to the current
flowing through it.
What is the SI unit of resistance
ohm (Ω).
The greater the ratio of V to I, the
greater the
resistance.
The resistance of an object depends on factors such as
the cross-sectional area, length and type of material the
object is made of.
What are fixed resistors
the
resistance of the circuit cannot be changed
unless the resistors themselves are changed.
the resistance of the circuit cannot be changed
unless
the resistors themselves are changed.
In a series circuit, the electrical components are joined one after another to form a single loop. Electric current passes through a single path in a series circuit.
one after another to form a single loop. Electric current passes through a single path in a series circuit.
A variable resistor or rheostat allows us to
adjust the resistance in a circuit.
In a parallel circuit, the electric current is divided into
into branches. Electrical components (e.g. bulbs) are connected in each branch. Electric current passes through all branches of a parallel circuit.
The higher the resistance, the
dimmer the bulb
When the rheostat slider is on
the left, the
short
resistance wire offers
low resistance.(bulb is brighter)
In a series circuit, the current at every point is …
the sum of the potential difference across
each component is equal to …
Vε = V1 + V2 + V3 + … + Vn
the same; , the potential
difference across the whole circuit.
In a series circuit, the effective resistance R is the
R = R1 + R2 + . . . + R
sum of all the resistances.
In a series circuit, the effective resistance is always
greater than the largest of the individual resistances.
V = IR
V: voltage (V)
I: current (A)
R: resistance (Ω)
What can an electric current cause when it is passed through certain liquids? What is the chemical effect used in?
-An electric current can cause a chemical
change when it is passed through certain
liquids.
-This chemical effect is used in electrolysis
and extraction of metals.
For n resistors placed in parallel, the effective
resistance R is given by
1/r = 1/r 1 + 1/r2 + 1/r3 …
then aft that the ans
r/num
e.g. 1/3+1/3 = 2/3
resistance = 3/2
the potential difference across each branch
is equal to
the potential difference across
the whole circuit.
In a parallel circuit, the sum of individual currents in each of the
branches
Iε = I1 + I2 + I3 + … + In
is equal to the main current.
What is electrolysis
Electricity can be used to break down
(decompose) compounds into its elements.
This process is called electrolysis.
An electric current has an effect on … this effect can be seen when
magnets.
This effect can be seen when an electric
current flows near a compass.
The magnetic effect can be increased by making
current flow in a coil of wire called a
solenoid.
The power of a circuit component is
the
amount of electrical energy converted to other
forms of energy per unit time by the
component.
The SI unit of power is
watt (W)
What is electroplating
Many objects are coated with a metal by
immersing the object in a liquid and then passing
an electric current through the liquid.
This method of coating objects with metals is
called electroplating.
1 kW = 1000 W
The formula of energy =
energy = power X time
Hazards of electricity
electrical fires, electric shocks and electrocution
Safety features in the household electrical system
earth wire, fuse and circuit breaker
The … wire
(blue) is at 0 V.
neutral
The … wire (yellow
and green) is at 0 V. It
is connected to the
… or …
earth, ground or earth
The … wire (brown) is
at a high voltage. In
Singapore, it is at … V.
live, 240
which wire is connected to the fuse?
live wire
Where is the neutral wire connected to?
The bottom left of the plug
Where is the earth wire connected to?
The top middle part of the plug
electrical systems can produce effects like
heating effect, magnetic effect and chemical effect
What does a fuse do
The fuse makes use of the heating
effect of an electric current to switch
off a large current. A large current causes a short, thin wire in the fuse to heat up and melt.
A … can also cut off an electric
current. However, unlike a fuse, it does not need
to be replaced.
circuit breaker
A blown fuse should be …
after an electrical fault has been
rectified.
replaced
Why does a circuit breaker not need to be replaced?
When a damaged appliance or the damaged part
of the circuit is fixed, the circuit can be switched
on again using the circuit breaker.
