Term 2 2016 - Practice Questions

Explain ionising radiation

Ionising radiation has enough energy that during an interaction with an atom it can remove electrons. Thus it changes the atom to an ion. UV, x-rays and gamma waves have the ability to ionise atoms within our cells which can be extremely harmful.

A lady named Jo excavated another axe fragment in Japan which has an activity of 2 Bq. If the original sample should have 128 Bq, does Jo's discovery agree or disagree with the article? Explain your answer fully.

128Bq 1hl - 64Bq 2hl - 32Bq 3hl - 16Bq 4hl - 8Bq 5hl - 4Bq 6hl - 2Bq 6 hl = 6 x 5730 = 34380 years Since the article states that axes started appearing in Japan around 35 000 years ago, Jo's discovery agrees with the article (as her axe fragment is approximately 34 380 years)

To date the axe described in the article, the scientists used a technique called 'carbon dating'. If the half‐life of the radioactive isotope carbon‐14 is 5730 years, a) How many half‐lives must have passed for it to be dated as 45 000 years to 49 000 years? b) What fraction of the original sample would be radioactive now?

45 000 ÷ 5730 ≈ 7.85 half lives 49 000 ÷ 5730 ≈ 8.55 half lives Thus approximately 7.85 - 8.55 half‐lives have passed Note: the question gave a range, so your answer should have a range)

An archaeologist extracts a gram of carbon from an ancient axe handle and measures between 7 - 8 beta emissions per minute from the sample. A gram of carbon extracted from a fresh piece of wood gives off 15 beta emissions per minute. Estimate the age of the axe handle.

7 beta /15 beta ½ of fresh sample. therefore 1 half life has occurred. Therefore the axe is 5730 years old approximately.

What determines the decay in the nucleus?

Alpha - nucleus is too large Beta- too many neutrons Gamma- too much energy

Anna says that radio waves can be called sound waves and are the longest type of electromagnetic radiation. Evaluate her statement.

Anna is incorrect. Whilst radio waves are the longest type of electromagnetic wave, They are not sound waves. Sound waves are mechanical waves that require particles to vibrate.

Which will give a higher reading on a radiation detector - equal amounts of radioactive material that has a short half-life or long half-life?

As activity is a measure of the amount of decay per second, if both samples were emitting the same type of particle (ie α, β or γ- decay) the higher reading will be given by the material that has a short half-life. More or it has to decay in the same amount of time

Why is nuclear radiation classified as ionising radiation?

Because all three types of nuclear radiation has the ability to remove electrons from an atom. Alpha particles attract the electrons and can 'knock' them off. Beta particles repel other electrons and 'knock' them off. Gamma waves can 'strike' and electron and transfer its energy to it, which causes it to get excited and 'jump' off the atom.

The half-life of cobalt-60 is approximately 5 years. If a radioactive sample was measured to have an activity of 50 Bq originally, and is now measured to have an activity of 10 Bq, how old is the sample?

Between 10 and 15 years

Put the following into order of smallest wavelength to the largest wavelength: UV, Radio, Visible light, X-rays, Gamma, Microwave, Infra-red

Gamma, X-rays, UV, Visible light, Infra-red, Microwaves, Radio

In 1979 na fictitious horror movie was released. Its tagline was "in space, no one can hear you scream." Discuss whether you disagree or agree with this statement

I agree with this statement because sound waves are mechanical waves - which require matter particles for it to travel. In space, there are no particles thus sound cannot travel. OR I disagree with this statement because when humans are in space, they are often inside a rocket or space station - which do have air particles inside. Since sound waves need particles to travel (they are mechanical waves) you would be able to hear sound.

In an alpha decay equation

Mass number: decrease by 4 Atomic number: decrease by 2 What's added: alpha particle

In a beta decay equation

Mass number: stays the same Atomic number: increase by 1 What's added: beta particle

In a gamma decay equation

Mass number: stays the same Atomic number: stays the same What's added: gamma wave

Tracey knows that the music we listen to in our cars is sent from radio towers. But if sound has to move by vibrating particles, why can't we hear the music with our own ears outside the car without the radio?

Radio waves are not sound waves, they are in fact, electromagnetic waves. Radio waves are transmitted from towers in all directions and the radio in your car can tune into these. It then turns this information into sound waves.

_______________ have the largest wavelengths on the electromagnetic spectrum. They are a type of ___________

Radio waves, non-ionising radiation

What are three ways we can protect ourselves from radiation?

Shield, reduce exposure time, increase distance from source

Deb doesn't want to sit next to the microwave as she says it's too dangerous. Give some informed advice highlighting your understanding of the type of radiation and the ways to minimise risk.

Sitting next to the microwave isn't dangerous. Microwave ovens generate microwave waves from the electromagnetic spectrum to interact with water molecules, causing them to increase in temperature. It would be dangerous for you to sit in a microwave as the water molecules in your body would increase in temperature and your body couldn't cope. Sitting beside the microwave is not dangerous as nothing is being emitted. Also microwave waves are non-ionising, so they are not going to harm/change any cells.

Explain what a coal power station would do

The coal is burned and as a result, heat is released. It is used to boil water and the steam from the boiling water creates enough pressure to turn large electric generators. This creates ELECTRICITY! A power station uses fuel to covert the potential energy to electrical energy

If the half-life of carbon-14 is 5730 years, about what fraction of the original radioactive carbon-14 would you expect to find in: a) An aboriginal boomerang 11 500 years old? b) A human skull 23 000 years old?

a) 11 500 / 5730 2 half lives therefore ¼ of the original radioactive carbon 14 will be present. b) 23 000 / 5730 4 half lives therefore 1/16 of the original radioactive carbon-14 will be present.

An old arrow was found and thought to be 11460 years old. a) If that is true, how many half-lives have passed? b) If the arrow today would have an activity of 20Bq (decays per second), what would the activity be of the old arrow be now? c) If the activity of the found arrow was measured to be 5.5Bq, would you agree or disagree that the arrow is 11460 years old?

a) 11460 / 5730 2 half lives b) 20 Bq x ¼ = 5 Bq c) It may suggest that the sample is actually a little younger than thought but this is an approximate process. I agree because it is extremely similar to 5Bq and 0.5 Bq isn't going to make much difference

You have 64g of a radioisotope with a half- life of 5 days. a) How much of the radioisotope will be left after 5 days? b) How much will be left after 10 days? c) How many days will it take for the mass to decrease to 1g?

a) 64g→32g after 5 days b) 10 days = 2 half-lives. 64g→32g→16g c) 64g→32g→16g→8g→4g→2g→1g 6 half-lives = 6 x 5 days =30 days

State whether the following are a fuel or energy: a) Coal b) Nuclear c) Uranium d) Sun e) Biomass

a) Fuel b) Energy c) Fuel d) Energy/Fuel e) Fuel

Actinium-228 decays by emitting beta particles and has a half-life of 6 hours. If actinium-228 has an activity of 60Bq (decays per second) now, calculate the activity in: a) 6 hours. b) 12 hours.

a) If 1 half-life is 6 hours and the initial reading was 60Bq then after 6 hours which is the equivalent to 1 half-life there will be 30 Bq. b) 12 hours is 2 half-lives so there will be 60Bq→30Bq→15Bq after 12 hours

State the 2 types of waves and give an example of each

a) Mechanical waves - sound waves b) Electromagnetic waves - radio waves

State the wave that: a) Pass through flesh but are absorbed by teeth and bones. b) Are absorbed by water molecules and is used to cook food. c) We can see with our eyes. d) Is emitted from warm objects (and night vision goggles can detect it). e) Is emitted from some radioactive substances.

a) x-rays b) micro waves c) visible light d) infra-red e) Gamma