P4

Question 1

How do you generate static electricity?

Answer 1

By rubbing two insulating materials together so that electrons lave one material for the other leaving on positively charged material and one negatively charged material.

Question 2

What are some example of static electricity?

Answer 2

Dusting brushes can be charged using the plastic wrapper so that dust is attracted to the negative charge (the wrapper loses electrons)
Synthetic clothing

Question 3

How do you discharge static electricity?

Answer 3

A charged object can be discharged (have the excess charge removed) by earthing it. If you are charged then earthed you could get a shock.

Question 4

What are the problems of static electricity?

Answer 4

Nuisance: dirt and dust get attracted to insulators like TVs, some materials cling to your skin
Dangerous: flour mills and petrochemical factories have atmospheres with flammable gases or lots of oxygen so a discharge of static electricity (a spark) can lead to explosions. Also when static flows through your body to earth it is dangerous - lightening

Question 5

What is the term for the atoms on an ebonite rod that has received electrons from a cloth?

Answer 5

Negative ions

Question 6

How can you reduce the dangers of static electricity?

Answer 6

Correctly earthing appliances
Using insulation mats
Wearing shoes with insulating soles
Earthing lorries with flammable loads before unloading
Using anti static sprays, liquids and cloths

Question 7

How does spray painting using electrostatics work?

Answer 7

Paint particles are given a negative charge because electrons rub off from the nozzle
Particles repel one another
The car panel is positively charged
The paint attracts to the panel
The car receives an even coating and become neutrally charged

Question 8

What are smoke precipitators and how do they work using electrostatics?

Answer 8

They remove smoke particles from chimneys
Metal grids are out in the chimney and connected to a high potential difference (voltage)
The dust becomes positively charged when passing the grid
The dust particles are attracted to negatively charged plates above
The dust forms on the plates and fall back down

Question 9

How do defibrillators work using electrostatics?

Answer 9

They return the heart to its usual rhythm
Two oppositely charged paddles are put on the patients chest using gel
The current flows through the chest to make the heart contract

Question 10

What is a circuit?

Answer 10

A complete loop that allows an electric current to flow
Electrons flow from the negative to positive electrode but this was only discovered recently so the diagrams show the current flowing the opposite way

Question 11

What is resistance and what are fixed and variable resistors?

Answer 11

Resistance is how hard it is to get a current through a component in a circuit at a certain voltage. Measured in ohms
A fixed resistor has a constant resistance, the more ohms the smaller the current that flows through
A variable resistor has a changeable resistance. Also called a rheostat

Question 12

What is the relation of current, voltage and resistance?

Answer 12

For a given resistor, current increases and voltage decreases and vice versa
Voltage = resistance x current

Question 13

What is inside a plug?

Answer 13

Live wire carries current to the appliance at 230V
Neutral wire completes circuit and carries current away from the appliance
Earth wire stops the appliance from becoming live

Question 14

What colour is each wire inside a plug?

Answer 14

Live is brown
Neutral is blue
Earth is yellow and green

Question 15

What type of appliances have an earth wire?

Answer 15

Ones with outer metal cases/ conductors, if the case is an insult they are double insulated so they can’t become live and an earth wire isn’t needed

Question 16

How does earthing work?

Answer 16

A fault in the appliance causes the casing to become live
The circuit short circuits because the earth wire offers less resistance
The fuse melts and the circuit breaks

Question 17

How do fuses work?

Answer 17

A fault causes the current to exceed the fuses current rating (which is just above the normal current)
The fuse wire gets hot and melts or breaks
The circuit is broken

Question 18

What is the difference between a fuse and a circuit breaker?

Answer 18

A circuit breaker can be reset but a fuse must be replaced

Question 19

What is the power rating of a device?

Answer 19

How quickly the electrical energy is being transferred into another form within that device

Question 20

What do fuses and circuit breakers prevent?

Answer 20

Injury and death because the appliance can’t become live
Fires because they stop cables and flexes from overheating
Damage to the components of the appliance beauteous the current can’t flow too high

Question 21

What is ultrasound?

Answer 21

Sound waves with frequencies above the limit of human hearing (20,000Hz), travels in a longitudinal wave

Question 22

How can ultrasound be used?

Answer 22

In medicine because you can scan the body with ultrasound waves and create a picture of organs
You can use them to break down kidney stones because they vibrate and are passed out of the body by urine which avoids surgery
Measure the speed of blood flow
Detect gal stones and tumours
Pre natal scanning due to less risk than an X-ray

Question 23

How does ultrasound produce an image?

Answer 23

They are partially reflected at a boundary as the pass though different mediums and the time taken fort he reflection to be detected is used to calculate the depth of the surface they were reflected from.

Question 24

What are the advantages of ultrasound over X-ray?

Answer 24

It produces images of soft tissue

Doesn’t damage living cells

Question 25

What is radioactivity?

Answer 25

Radioactive materials give out nuclear radiation fro, the nucleus of each of their atoms. The atoms are unstable and decay naturally. During the decay radiation is given our in alpha, beta and gamma rays. Radiation is measured by the number of nuclear decays emitted per second. Ionisation occurs when uncharged atoms gain or lose electrons

Question 26

Why is alpha highly ionising?

Answer 26

It is missing two electrons (it has a charge of +2) so it attracts more atoms as it passes leaving them positively charged

Question 27

What happens during alpha emission?

Answer 27

The atom decay by ejecting an alpha particle (which is a helium nucleus with two protons and two neutrons) from its nucleus.
The nucleus of the new atom which is left is different to the original because it is a different element - it has two fewer protons and two fewer neutrons so the atomic number decreases by two and the mass number decreases by four

Question 28

What happens during beta emission?

Answer 28

The atom decays by changing a neutron into a proton and an electron. The high energy electron ejected from the nucleus is the beta particle. The new atom which was left behind is different because the nucleus has another proton and one less neutron so the atomic number has increased by one and the mass number is the same

Question 29

What is half life?

Answer 29

The time taken for the undeclared nuclei in a radioactive substance to decay and decrease radioactivity by half

Question 30

How can igneous rocks wth uranium atoms be dated?

Answer 30

The uranium decays to produce lead atoms so they can be dated by measuring the proportion of uranium to lead and by knowing the half life of uranium (about 4.5 billion years depending on the isotope)

Question 31

What is background radiation?

Answer 31

The radiation that naturally occurs, mostly through cosmic rays and radioactive substances in rocks and soil (a small percentage through industry and hospitals)

Question 32

What are tracers?

Answer 32

Radioisotopes are used as tracers to track the dispersal of waste and find leaks and blockages in underground pipes. The radioactive material that emits gamma rays is put into the pipe and the progress is measured at the surface

Question 33

How do smoke detectors work?

Answer 33

They contain americium 241 (alpha emitter) and the emitted particles ionise the air and the ions are attracted to oppositely charged electrodes to make a current. When smoke enters the space between the electrodes less ionisation takes place because the alpha particles are absorbed by the smoke particles, then a smaller current flows which triggers the alarm

Question 34

What is carbon dating?

Answer 34

Some carbon is radioactive carbon-14 and the activity of it can be used to find the age of a once living material. The amount of it in the atmosphere has stayed the same for thousands of years. A dead object doesn’t exchange gases as much with the air as living matter does. As the carbon in the dead object decays it isn’t replaced so the radioactivity of the sample decreases. The dead object has a lower amount of carbon if it is older and the ratio is used to see how old it is within the limits (about 50 years)