Flashcards in Electricity Deck (20)
What is charge measured in?
There are how many types of charges and list them
Negative and positive
Unlike charges ...
Like charges ...
What is an electric field?
a region in which an electric charge experiences a force
Describe simple experiments to show the
production and detection of electrostatic charges
Get a balloon.
Rub the balloon quickly on any dry surface e.g. a carpet.
Go to the nearest faucet/ water tap.
Turn it on.
Place the balloon close to but not touching the running water. ( see that the water bends towards the balloon)
State the direction of lines of force and
describe the field around a point charge and the field
between two parallel plates
A line of a force is the path of a free positive charge released in an electric field
The field around the point (diagram fig.11.2.2 pg 156)
The lines of force between 2 oppositely charged parallel conductors are parallel to another
Definition of current, voltage and charge
Current: rate of flow of electrons, represents how much electric charge is passing a single point in the circuit in moment (A)
Voltage: energy per charge (V)
Charge: amount of positive/negative (Ohms)
Distinguish between the direction of flow
of electrons and conventional current
Direction of flow: from - to +
Conventional current: + to -
Current equation (2)
I = V/R
I = Q/t
Voltage current (2)
V = IR
V = E/Q (E is energy)
R = V/I
What is electromotive force (e.m.f)?
energy supplied by a source in driving charge round a complete circuit
Electrical energy equation
P = IV
no voltage: P = IxIR
no current: P = VxV/R
How changes in p.d. or current affect resistance
↑ in Voltage = ↑ in resistance
↑ in Current = ↓ in resistance
Relationship between resistance and length; resistance and cross-sectional area of a wire
To increase resistance, make the wire:
- Longer (length) => directly proportional
e.g. the longer the pipe, the more energy one must put into delivering water along its full length
-Thinner (diameter) => inversely proportional
e.g. the wider the pipe is, the easier it is to pump water through it and vice versa => make it thin
In a series circuit,...
Calculate combined resistance of two or more resistors in series
- Current is the same. I1 = I2 = I3
- Voltage is shared. p.d.s across the components in a series circuit is equal to the total p.d. across the supply. Vt = V1 + V2
- Resistance: Rt = R1 +R2
In a parallel circuit,...
Calculate combined resistance of two or more resistors in parallel
- Current: the current from the source is the sum of the currents in the separate branches. It = I1 + I2
- Voltage is the same
- Resistance: 1/Rt = 1/R1 + 1/R2
Describe the action of thermistors and lightdependent
resistors and show understanding of
their use as input transducers
- Transducers are devices that convert one type of energy into another.
- Thermistors :temperature increase => resistance decrease. Thermistors are often used as current limiting devices that help prevent over heating. Once the current gets to a certain limit (increasing heat lowers resistance, leads to increasing current), the circuit is broken to prevent overheating.
- Light-dependent resistors: increasing light intensity => lowering resistance. LDRs can be used on street lamps as input transducers. In this case, when it gets dark, the street lamps turn on.
Describe the action of a variable potential divider
Consists of 2 or more resistors in series connected to a fixed pd. Used to share/divide pd between resistors