BMAT Section 2 - Physics

What is temperature a measure of

The average kinetic energy of the particles in a substance

How to make the rate of cooling faster

The greater the difference in temperature between objects

How to make energy flow between places

If there's a difference in temperature between the two places

How does boiling occur

Big bubbles of gas form when particles have enough energy to overcome their attraction to eachother

What are melting and boiling points affected by

Impurities

When substances are condensing or freezing what happens to energy and temp

Energy is released and temp does not go down till all the substance is liquid/solid

What happens to most substances when heated

Expand and volume increases

What does conduction mainly occur in

Solids

What happens when one particle vibrates in solids

Bumps into others and passes vibration on

What is conduction of heat

Vibrating particles pass know extra ke to neighbouring particles

Why do metals conduct heat well

Free electrons inside metal

Why are non metals good at insulating

Don't have free electrons

How does surface area effect the rate of conduction

Larger means more room for collisions

Is current used up as it flows around the circuit

No

As you move up the alkane series, whay happens to the boiling point,viscosity, flammability amd volatility

Boiling point and viscosity increases; flammability amd volatility decrease

What happens when two insulating materials are rubbed together

electrons are scraped off one and dumped on the other

What charge is left on each of the insulating materials that have been rubbed

postive - on one when electrons scraped of; negative- on one where electrons dumped

Example of rubbing insualting materials

polyethene rod/acetate rod rubbed with a cloth

What happens when the polyethene rod is rubbed with a cloth

electrons move from duster to rod

what happens when the acetate rod is rubbed with a cloth

electrons move from rod to duster

How is a positive static charge formed

electrons moving away from object

How do static electricity form

electrons are all dumped on to one of the insulating objects; which repel each other but can't move away resulting a a patch of charge (static electricity)

Real life static electricity occurances

1) Attracting dust; dust tiny attract to anything charged
2) clinging clothes and crackles; e.g dragging a jumper over head electrons scrapped off
3) bad hair day; static build up on hair, each strand the same charge and repel eachother

Dangers of static electricity

1) Build up on clothes resulting in spark - bad near fuel fumes/inflammable gases
2) fuel flows out filler pipe, or paper dragged over rollers, or grain shoots out of pipes; static build up dangerous

How to prevent static build up

insulating, earth fuel tanks, anti-static sprays

How do paint sprays work

Paint is given same charge so every droplet repels from each other, the object to be painted is given the opposite charge so paint attracts - results in a fine, even coating and no paint waisted

How do dust precipitators clean emission

Use static electricity to clean up emissions, dust particles become neg. charge as they pass through a charged wire grid, neg. charged dust particles then stick to earthed metal plates - eventually fall to the bottom; where they can be removed

What is electric current

flow of charge

What are the conductors and insulators like in an electric circuit

metal conductors - full of charges (electrons) that are free to move

insulators e.g. plastic - current can't flow because few free charges

What happen to the charges in a complete circuit - role of battery

battery pushes the free charges through the wires; charge flows all the way round and back to the battery

When will current (I) only flow through a component

When there's a voltage

Unit for current

Amperes (amps) A

What is voltage

the driving force that pushes the current around

Unit for voltage

Volts (V)

What causes resistance

Things in the circuit (components e.g lamps,)

What do resistors do in a circuit

resist the flow of charge

Unit for resistors

ohms

What is power

the rate of energy transfer

Measure of power

watts (W) or kilowatts (kW)

What does an appliance with a high power rating do

transfer a lot of energy in a short time

Where can a voltmeter be placed

in parallel around the component under test

What does a voltmeter measure

the potential difference between two points

What is potential difference

tells is how much energy is transferred to or from each unit of charge as it moves between two points

What happens when energy is transferred

work is done

What does the voltage of a battery tell

how mcuh work the battery will do

Why must the voltmeter be placed in parallel to the component being tested

compare the energy the charge has before and after passing through the component.

What does the slope of a voltage-current graph show

How the current in a circuit varies as you change the voltage - resistance

So the steeper the slop in a V-I graph what does it mean for its resisitance

lower

What happens to resistors when current passes through them

gets hot

Why does a resistor get hot when current passes through

electrons collide with the station positive ions in the resistors making the ions vibrate more; increases in temp.

what is an LDR

light dependent resistor - bright light, resistance falls vice versa

Uses for LDR

automatic night lights

What is a thermistor

temp-dependent resistor - in hot conditions, the resistance drops

How are the components in a series circuit arranged

in a line, end to end

What happens to the PD in a series circuit

it is shared between each component, so it adds up to equal the PD across the battery

Why is PD shared in a series circuit

the work done on the charge by the battery must equal the work done by the charge on the components

What happens to the current in a series circuit

same everywhere.the same current flows through all parts of the circuit

What is the size of the current determined by

the total PD of the cells and the total resistance of the circuit

What happens to resistance in a series ciruit

total resistance is the sum of the individual resistances

What happen to the PD when the resistance of one component changes

PD across all the components changes

What happens to the cell voltages in a series circuit/parrallel

Adds up/ done add up in parallel

Why do cell voltages add up in a series circuit

bigger total voltages is several cells connected in a series, in the same way because each charge gets a push from each cell in turn

What happens to cell current in a series/parallel

but does add up in a parallel

Why does;t cell current add up in a series circuit

Max current is the same but in parallel; total current increases but current through each cell is less then total because they join to make total

What is a parallel circuit

each componented is connect separately to the +ve and -ve supply - in parallel

How is PD across all componenet

the same; V1=V2=V3, so identical bulbs connects in parallel will have the same brightness

How is total current in a parallel ciruit

shared between each branch
A=A1+A2

How is total resistance of a parallel circuit

LESS than that of the branch with the smallest resistance

Why is resistance lower in a parallel circuit

the charge has more than one branch to take- only some of the charge will flow along each branch

What are transformers

Used to change the size of the voltage - use electromagnetic induction to 'set up' or 'step down' the voltage. they have two coils of wire, the primary and secondary around an iron core

What happens in the primary and secondary coils

alternating current in primary causes changes in the irons core magnetic field, which induces a changing voltage int he secondary coil

What is the difference between step up and step down transformers

step up - increases voltage - more turns on the secondary coil vice versa

How does a transformer work

1) primary coil induces a magnetic field which stays within the iron core
2) AC in primary, magnetic field in the iron core always changing direction
3) changing magnetic field induces an alternating voltage in the secondary coil
4) no. of turns on two coils determines whether the voltage induced in the secondary coil is greater or less than the voltage in the primary coil
5) Is DC to primary - then no alternating magnetic field and won't work

What is a magnetic field

a region where the magnetic materials and also wires carrying currents experience a force acting on them

magnetic field from a current carrying wire

In concentric circles around the wire

What does a rectangular coil wire do to a magnetic field

Reinforces it; two sets of circular magnetic fields reinforces eachother

How can magnetic fields make current-carrying coils turn

Rectangular coil of wire carrying a current is placed in a uniform magnetic field, force will cause it to turn - moto effect

What's a generator

A coil rotating in a magnetic field

How does a generator work

As the coil spins, a current is induced in the coil, this current changes direction every half turn - AC voltage produced - faster revolution more peaks and higher voltage - higher currents induced when coil is perpendicular to the magnetic field -

What is meant by transformers are nearly 100% efficient

power in = power out
so... VpIp=VsIs

What is speed

distance travelled in a certain time

What is velocity

speed in a given direction

What is distance in a particular direction

displacement

distance time graphs: gradient=
flat sections=
curves=

gradient = speed
Flat section = stationary
Curves = acceleration/decelleration

What is acceleration

How quickly you're speeding up - change in velocity (speed) in a certain amount of time

Velocity time graphs
Gradient=
flat=
Area under any section=
curve=

gradient = acceleration
flat = same speed
area = displacement
curve= changing acceleration

How to work out acceleration from velocity-time graph

vertical/horizontal

What is happening to an object laid at rest in terms of newtons first law (forces)

Object pushes downwards on the surface and at the same time the surface pushes up the same amount; two forces are the same size so arrows are too

Explain an object moving at a steady speed in terms of forces

Forces are balanced; equal thrust, reaction, drag and weight

What is the resultant force

The overall force acting on an object; force you get when you take into account all the individual forces and their direction

What does the resultant force determine

whether it will accelerate, decelerate, steady speed

Why does accelerating not always mean a change in speed

could mean a change in direction - as its velocity

What will happen if a car exerts a bigger driving force than the drag counter force

it will accelerate

The bigger the resultant force then what does this mean

the bigger the acceleration

What is momentum

how much "oomph" an object has - how hard it'd be to stop it moving

So what would make it hard to stop something

the heavier it is, faster its moving

What is the conservation in momentum

the momentum lost by an object is equal to the momentum gained by another object on collision; so no momentum is lost

What is newton's second law

The acceleration of an object is dependent on the net force acting on the object and the mass of the object

Difference between mass and weight

mass - how much matter object is made up of
Weight- how much gravitational pull an object has

What is g

the acceleration due to gravity - gravitational field strenght