physics m1

Why does friction cause an object to become negatively charged?(static electricity)

Transfer of electrons from one object to another

Why does a negatively charged person experience a shock when they touch something?

There is a potential difference between them
Electrons transfer FROM the charged person
Which earths the charge

Why do conductors decrease the electric shock that someone faces if they are negatively charged?

Material has a low resistance
So there is smaller potential difference between objects

RP3 - how does the resistance vary with length in circuits

Measure the length
Vary the length each time
Measure the current and potential difference each time
Repeat readings
Calculate resistance at each length
Formula
Plot a graph of resistance against length
Hazards: high current may cause skin burns so use low current

Why does switching the circuit off between readings improve accuracy?(RP3)

The temperature of the wire would not change

How does resistance of a component change as potential difference increases across it?

The current increases
Temperature of the filament increases
So the resistance increases

What does more energy efficient mean?

A higher porportion of the total energy is usefully transferred

For an LDR, what happens to the potential difference and current when the light intensity decreases?

Potential difference increases, current decreases

Why is it safe to use a source of alpha radiation in a house?

Alpha radiation does not penetrate skin

Explain the ideal properties of a radioactive source for use in medical diagnosis

short half life or half life or a few hours means less damage to body
Low ionising power also means this
Highly penetrating means it can be detected outside the body

Why does taking repeat readings provide more accurate data?

You can calculate a mean
You can identify and remove anomalies

What type of error would be caused if the student’s eye was not in line with the level of the liquid in the tube during a measurement?

Random error because eye position would not be the same each time relative to the liquid

Explain how a temperature increase would affect the pressure exerted by the gas

It would increase the pressure in a tube even if the volume was constant
Because it would mean higher average kinetic energy of particlesW

What would doing work on an enclosed gas lead to?

Work is done on the air so the temperature of the air increases

What are the advantages of nuclear power?

No carbon dioxide emitted
Doesn’t cause global warming
More energy released per kg of fuel

Describe the process of nuclear fission

a neutron is absorbed by a nucleus
the nucleus splits into two nuclei releasing energy, gamma rays, and neutrons

What does power mean?

Energy transferred per second

Required practical 2

Set up the apparatus by placing a small beaker inside the larger beaker

Fill the small beaker with boiling water from a kettle

Place a piece of cardboard over the beakers as a lid. It should have a hole suitable for a thermometer and place the thermometer through this hole and into the water in the small beaker

Record the temperature of the water in the small beaker and start the stopwatch

Record the temperature of the water every 2 minutes for 20 minutes, or until the water reaches room temperature

Repeat the experiment, each time changing the cardboard for another insulating material (in any order) and also without any insulation at all

Explain why contamination of the inside of the human body by a radioactive material that emits alpha radiation is highly dangerous.

Alpha radiation is highly ionising causing an increased risk of cancer until the radioactive material is removed

What is the frequency of the mains electricity supply in the UK?

50 hz

Why do switches need to be on?

So charge can flow

When moving down, why is increase in kinetic energy is less than decrease in gravitational potential energy.

Work done against air resistance means some thermal energy is transferred to the surroundings

What is the force when a balloon rubs on a person’s hair?

Electrostatic attraction between hair and balloon

How does internal energy of a liquid change as it is heated(no state change)?

Mean kinetic energy of particles increases
Which increases internal energy of substance

How is the particle model used to explain the difference in density between a liquid and a gas?

Particles in a gas have more potential energy than particles in a liquid.

What is a zero error?

When the equipment doesn’t measure 0 if the actual value is 0

Advantages of using gas to produce electricity compared to coal

Doesnt cause acid rain
NO sulfur dioxide released
less co2 per kg of fuel released
Less global warming
No solid waste

What are the natural sources of background radiation?

Rocks, cosmic rays from spaceW

What are the manmade sources of background radiation?

Chernobyl
X rays
CT scans
Radiotherapy

Name one nuclear fuel

Thorium, uranium, plutonium

Describe the process of nuclear fission inside a nuclear reactor

Neutron absorbed by uranium nucleus
Nucleus splits into 2 parts
And 2/3 neutrons release
And gamma rays are emitted

How does nuclear fusion release energy?

Lighter nuclei join to form heavier nuclei
Some of the mass is converted to energy

Explain the advantage of radioactive waste having a shorter half life

Activity decreases quickly, risk of harm reduces quickly

What happens at the bottom of a slide?

Decrease in GPE = decrease in kE
v² = 2gh(masses cancel)
Final speed only depends on vertical height, gravity is constant
Variations are due to air resistance/friction

What is precision?

When there is little variation in the data

Why does adding resistors in parallel decrease the total resistance?

Multiple paths for charge to flow
Total current is greater for the same voltage

What happens if you touch a live wire?

If you are earthed, there is a large potential difference between the live wire and you

Why does gas pressure increase if it is compressed?(Other factors constant)

Particles would have higher mean Ke
Increased number of collisions with the walls per second
Greater forces exerted in collisions
Greater force exerted on same area

What does direct potential difference mean?

The polarity does not change

Explain one environmental effect of using fossil fuels to generate electricity

Carbon dioxide causes global warming

RP4: Investigate how the current in resistor R at constant temperature varied with the potential difference across the resistor

Measure the current in R using the ammeter
Measure the p.d across R using the voltmeter
Vary the resistance of variable resistor
Record a range of values of current and p.d

Ensure current is low to avoid temperature increase

What is meant by the random nature of radioactive decay?

You cant predict which nucleus will decay next

When volume increases, why does pressure decrease?

There are less frequent collisions between particles and walls
Causing a lower average force on the walls
And pressure is total force per unit area

Explain the advantage of transmitting electricity at a very high .d

Very high p.d means low currents
Which means less energy is transferred to the surroundings
Which increases the efficiency of power transmission

Why could you be fatally shocked if your kite was close to, but not touching a power cable?

Electric field strength is very high
Causing the air to become ionised
The kite conducts charge to the earth

Explain why current in a steel wire is different to current in an aluminium wire

Potential difference across all wires is the same, but the resistance of steel wires are greater so there is less current in the steel

Method for measuring the density of an irregular rock

Measure mass using a balance
Part fill a measuring cylinder with water and measure initial volume
Place rock in water and measure final volume
Volume of rock = final volume - initial volume
Fill a eureka can with water level with spout
Place a rock in water and collect displaced water
Measuring cylinder used to determine volume of displaced water
Volume of rock = volume of displaced water
Density = mass/volume

Why would taking more than one measurement in a practical increase accuracy?

A mean can be calculated which reduces the effect of random errors

Why would a non-digital thermometer be harder to read?

Viewing angle affects measurement

What does it mean if a material decreases by the same temperature as another material but at a shorter time?

Higher thermal conductivity because the rate of energy transfer is higher

When insulators are rubbed together, why do they become charged?

Electrons are transferred from one to the other
Electrons are negatively charged
So there are more positive than negative charges on the original object

A negatively charged rod is held near an earth conductor. Explain why a spark jumps between the negatively charged rod and the earthed conductor.

Large potential difference between the 2 objects
Causes electrons to move through the air from the rod to the conductor

Why are step up transformers used in the national grid?

It increases potential difference and decreases current
Reducing energy transfer to the surroundings
Increasing the efficiency of power transmission

Why are step down transformers used in the national grid?

It decreases the potential difference to a safer value

What does an alpha particle consist of?

2 protons and 2 neutrons
Helium nucleus

Explain how the risk from internal contamination is different to the risk from external irradiation by a source of alpha radiation.

Alpha radiation has a low penetrating ability
So external alpha radiation is stopped by skin(therefore it is low risk)
internally, alpha radiation is absorbed by living tissue/organs
as alpha radiation is highly ionising, internal contamination will cause greater risk of harm to cells(and greater chance of mutations)

Explain the changes in the arrangement and movement of the particles as ice melts and the temperature increases from 0 degrees celsius to 5 °C.

Particles in a solid are in a regular pattern
Particles in a liquid are in a random arrangement
Particles in a solid are vibrating about fixed positions
Particles in a liquid are moving freely
As the ice changes to water the temperature remains constant
Because the potential energy of the particles increases
As the water warms the particles move faster
So the kinetic energy of the particles increases
Internal energy is the total kinetic and potential energy of all the particles

Compare the structure of an atom of carbon-14 to the structure of an atom of carbon-12

Similarities: Same proton and electron number
Differences: different neutron numer

What does a lower half life mean for safety and why?

The lower the half life, the higher the activity so a greater dose of radiation is absorbed per second

What is the difference between irradiation and contamination?

Irradiation - exposure of an object/person to radiation
Contamination - unwanted presence of radioactive material on an object

Why do workers need to stand close to radiation detectors?

Some radioactive materials emit alpha radiation
which has a very short range in air

Why would an alpha particle bounce off a sheet of gold leaf?

Both the alpha particle and gold nucleus have the same charge so the alpha particle and gold nucleus repel each-other

How is the bohr model of the atom different to the nuclear model of the atom?

In the bohr model electrons orbit the nucleus at specific distances whereas in the nuclear model the electrons can orbit at a specific range of distances

Explain how an electron can move up and down between energy levels in an atom

To move to a higher energy level an electron absorbs energy from electromagnetic radiation
To move to a lower energy level an electron emits energy in the form of electromagnetic radation

Explain why pressure increases when more air is pumped into a tyre

More air particles in the tire
Greater number of collisions with the tyre wall per second

The air pressure in a car tyre changes if the temperature of the air in the tyre increases. Explain why

Air particles have greater mean kinetic energy
So more collisions with the tyre walls per second
And greater force in each collsiion
Greater force per square meter causes greater pressure on the wall of the tyre

Describe the movement of particles of helium gas inside a balloon

Range of speeds
Moving in different directions

Explain what led to the plum pudding model of the atom being replaced by the nuclear model of the atom.

alpha particle scattering experiment
alpha particles directed at gold foil
most alpha particles pass straight through
(so) most of atom is empty space
a few alpha particles deflected through large angles
(so) mass is concentrated at centre of atom
(and) nucleus is (positively) charged
plum pudding model has mass spread throughout atom
plum pudding model has charge spread throughout atom

Explain how an uncharged object may become positively charged

negatively charged electrons are transferred from the (neutral) object