Questions Flashcards
What does lubrication do to surfaces
It reduces the surface friction between objects this slows down wear also
What is a system
An object or group of objects
Types of lubricant ion
Lubricant
Oil in a motor reduces friction so less energy is lost as thermal energy
Properties of thermal conductivity
Higher the thermal conductivity of material means heat travels through object more easily so higher rate of energy tranfer by conduction through material
Thermal conductivity in building
Rate of cooling is low if walls are thick
If walls are thing metal sheets hear would be lost very quickly
What are the trends of the energy use
During Industrial Revolution fossil fules became important as they were easy to mine and provided lots of energy
How does resistance change
With current
With current
As current increases charge has more energy
It makes it more difficult for electrons to follow through the resistor so resistant mice increases and current decreases
How does the resistance change with temp
Thermistor
In hotter temperatures the resistance is lower
These are often used in temperature detectors/thermostats
How does resistance change with length
The greater the length, the more resistance and the lower the current
o Electrons have to make their way through more resistor atoms,so itis harder than
using a shorter wire
How does resistance change with light
LDR(LightDependentResistor)
The greater the intensity of light, the lower the resistance
So the resistance is greatest when it is dark
These are used in automatic night lights.
How does resistance change with voltage
Diodes
Diode allows current to flow freely in one direction
In the opposite direction, it has a very high resistance so no current can flow
Properties of series circuit
- Series Circuits
o Closedcircuit
o Current only follows a single path
o TotalResistance= all resistors added up
o The current is the same everywhere
Properties of parralel circuit
Parallel Circuits
o Branchedcircuit
o Currentsplitsintomultiplepaths
o Total current Into a junction=total current in each of the branches
o The potential difference is the same across each“branch”
Why is the resisters in parralel less than then the lowest resisters
Two resistors in parallel will have a smaller overall resistance than just one
Because charge has more than one branch to take, so only some charge will flow along each branch
What is ac and dc
AC is alternating current, which comes from the mains
Currentcontinuouslyvaries,from positive to negative (charge changes direction)
- DC, direct current, is the movement of charge in one direction only o Cells and batteries supply direct current
What are the 3 wires
Live-wire-230 volts
Carries the alternating potenitiql differnce from the source
Neutral blue at 0V
Completes the circuit
Earth wire
Green and yellow wires only carries a current if they’re a fault
Safety wire to stop the appliance from becoming alive
Properties of the transformers
Step-upTransformers
Increase the pd from the power station to the National Grid
So as the power is constant current decreases so less energy is
lost.
Step-upTransformers
Increase the pd from the power station to the National Grid
So as the power is constant current decreases so less energy is
lost.
How does spacing between atoms depend density
- Gases have a far lower density
o The spacing between atoms increase x10, as the particles
have lots of energy to move,
Solids and liquids have similar densities as the space between particles does not change significantly
Properties of em radiation from atoms
When electrons change orbit (move closer or further from the nucleus)
o
When electrons move to a higher orbit(further from the nucleus)
The atom has absorbed EM radiation
o When the electrons falls to a lower orbit(closer to the nucleus)
The atoms has emitted EM radiation
- If an electron gains enough energy, it can leave the atom to form a positive ion
Forms of decay
Alphaα(aheliumnucleus) Highly ionising
Weakly penetrating (~5cm of air)
o BetaMinusβ(electron) Medium ionising
Medium penetration (few meters of air, sheet of aluminium )
o Gammaγ(radiation) Low ionising
Highly penetration (several meters of concrete and few cm of lead )
Properties of half life’s
The half-life of an isotope is the time taken for half the nuclei in a sample to decay or the time taken for the activity or count rate of a sample to decay by half.
It cannot be predicted when any one nucleus will decay
How is alpha radiation used in smoke detectors
It is an alpha emitter, and used in smoke alarms
It is emitted into the air around the alarm, and does not reach far because alpha is weakly penetrating
If smoke reaches the alarm, the amount of alpha particles in the surrounding air drops
This causes the alarm to sound
What is contamination
Lastsforalongperiodoftime
o Thesourceoftheradiationistransferredtoanobject
Radioactive contamination is the unwanted presence of radioactive atoms on other materials – the hazard is the decaying of the contaminated atoms releasing radiation
o E.g.radioactivedustsettlingonyourskin
What is iridaition
- Irradiation
o Lasts only for a short period of time
oThe source emits radiation,which reaches the object
Exposing an object to nuclear radiation, but does not make it radioactive E.g.radio active dust emitting beta radiation,which“irradiates”yourskin
o Medical Items are irradiated sometimes to kill bacteria on its surface,but not to
make the medical tools themselves radioactive
What is boyles law
Boyle’s law is a gas law, stating that the pressure and volume of a gas have an inverse relationship. If volume increases, then pressure decreases and vice versa, when the temperature is held constant
