P2 Flashcards
What is a series circuit?
Series circuit has no branches and the current can only flow in one path
What is current?
An electric current is a flow of electric charge around a circuit
Unit amp(a)
How do you measure Current?
You can measure current in a circuit by using an ammeter
What is a parallel circuit?
A parallel circuit contains branches and splits currents between branches
What is the current like in the parallel circuits?
The current in the branches adds up to the total current leaving the cell
What is potential difference?
measure of energy, per unit of charge, transferred between two points in a circuit
What we used to measure potential difference
Volt meter
What is the potential difference in parallel circuits like?
For components connected in parallel the potential difference across each component is the same
what is electrical charge
Electric charge is an amount of electricity that is held in or carried by something.
a current of one amp = 1 coulomb of charge flowing per second
what is the equation for charge flow
q=lxt
charge flow =currentxtime
What is resistance ?
Resistance tells us the potential difference required to drive a current through a component
What is the equation for energy transferred?
E=QxV
Energy transferred (G) = charge flow (C) x potential difference (V)
What is the equation for resistance?
R=V/I
Resistance=pd/current
what is DC?
direct current produced from a cell
what is an AC?
- Alternating current and an example is uk mains
- in uk AC frequency is 50Hz
-PD is 230 volts
what are benifits of AC?
- very easy to use a transformer to increase or decrease the pd
what is the brown live wire used for?
-carries the alternating potential difference from the supply(230v)
-connected to the fuse in the plug
what is the blue neutral wire used for?
completes the circuit and has a pd of 0 compared to the live wire
what is the green and yellow safety wire used for?
-stops the appliances from becoming live
what is the national grid?
the national grid consists of a system of transformers and high voltage cables
what does a step up transformer do?
increase potential difference to several hundred thousand volts so less energy is lost within the power cables
what is uncertainty
due to random error scientists cannot be certain of the accurate or true value of measurement
how do we calculate uncertainty
range of values/2
what is the equation that links power current and resistance
power=current^2 x resistance
what is the resistance of an LDR like
-Resistance of an LDR is low in the light
-Resistance changes depending on light intensity
what happens to the ammeter in a circuit if resistance of the circuit decreases
-more current is allowed to flow through the circuit
what happens to the voltmeter if the resistance of the component its reading decreases
-the voltmeter would get less share of PD
-the reading of the voltmeter will decrease
how should we change the circuit to give negative values for current and PD
reverse connections to the cell
relationship between current and pd for a resistor at constant temp
directly proportional
differences between AC and DC
-direct current is always in the same direction
-alternating current changes direction
when connecting to the uk mains why is it beneficial to use a low resistance cable
-lower potential difference across
the cable
-it is more efficient
calculation for resistance
PD/current
what is the resistance of resistors connected in parallel
the total resistance of two resistors in parallel is less than the resistance of the smallest individual resistor
student increased the temperature of the thermistor.
Explain how the current in the thermistor changed.
-the current increased
-(because) the resistance (of the
thermistor) decreased
The heating element of the kettle was connected to the mains supply.
Explain why the temperature of the heating element increased.
-electrons collide with particles in
the heating element
-which increases the (kinetic)
energy of the particles
measuring using a geiger muller tube
explain why count rate of a radioactive sample is less then activity
-the source spreads radiation in every direction
-the geiger muller tube only measures the radiation that passes through
