FW:

1. Moons orbit planets but the planets orbits the sun.
2. No some planters have more than one moon for example, Jupiter has 66 moons.
3. Yes they do because if you go there you will be able to stand on it.
4. Jupiter has the biggest gravitational field ok 26N/kg which is 2.6 more than earth's gravitational field.
5. Mercury and Mars both have a gravitational field of 4N/kg.
6. The smaller the planet the weaker the gravitational field strength.
7. Mercury has the smallest time of orbit which takes 3 months.
8. The planet with the longest orbit is Neptune and it takes 1978 months to orbit the sun.
9.The further away the planet the longer it takes of the planet to orbit the sun.
10. The closer the planet is to the sun the hotter it is, except for venus being hotter than mercury because mercury does not have a atmosphere.
11. There are four inner and outer planet, the four inner planters are small and rocky, the outer planets are large and glacius and far from the sun.
12. A comet has two tails. They are made out of dust and ice.
13. The orbits of the asteroids are highly elliptical and the orbits of the comets are circular.
14. Pluto is no longer a planet.

7.15 HOMEWORK

7.15 and 7.16 Plenary Answers

1. How are alpha particles deflected by the "Plum Pudding Model"

The alpha particles are not deflected - they pass straight through

2. How are alpha particles deflected by "Rutherford's Nuclear Model"

· Most alpha particles are undeflected and pass straight through
· Some alpha particles are deflected through a small angle
· A few alpha particles are deflected through a large angle

3· What happens if you increase the speed of the alpha particles?

The amount of deflection decreases as the alpha particles have more Kinetic Energy to overcome a greater amount of Electrostatic Potential Energy of their repulsion with the nucleus.

4. What happens if you increase the charge of the nucleus?

The amount of deflection increases as there is now greater electrostatic repulsion between the nucleus and the alpha particle

5. What happens if you increase the number of neutrons in the nucleus?

The amount of deflection is unaffected (increasing the number of neutrons does not affect the charge on the nucleus)

7.10 to 7.12

7.10 to 7.12 starter

· Smoke detectors use 241Am to emit alpha particles which pass through a small air gap before being detected. If smoke particles are present they interrupt the beam of alpha particles and this triggers the alarm to go off
· Tomorrow, will the 241Am still be as radioactive?
· Next year, will the 241Am still be as radioactive?
· In a thousand years, will the 241Am still be as radioactive?

Answers
· To answer the questions, we need to know the half life of Americium-241 which is 432 years
· Tomorrow and even next year its activity will hardly have changed at all (sensible for a smoke detector - you don't want it to suddenly stop working!)
· In a thousand years its activity will have dropped to about a quarter

7.10 to 7.12

12 January 2012

10:24
· 7.10 understand that the activity of a radioactive source decreases over a period of time and is measured in becquerels
· 7.11 recall the term ‘half-life’ and understand that it is different for different radioactive isotopes
· 7.12 use the concept of half-life to carry out simple calculations on activity

Half-life of Different Isotopes
· http://youtu.be/S-goxH05LbY
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interactive simple half life calculations.swf Download this file

Half life.pptx Download this file

Decay of Balonium - exponential graph.swf Download this file

QUESTIONS HOMEWORK

1. What happens to the amount of ‘mother’ nuclei as time passes?
Decrease

2. What sort of radioisotope will decay the fastest - one with a long half life or one with a short half life?
One with a short half life

3. Does half life tell us exactly when a particular nucleus in a radioisotope will decay?
No. It is a random process - we can not know exactly when a particular nucleus will decay

4. What are the two definitions of half life?
a. The time taken for the activity of a sample to halve

b. The time taken for the number of radioactive atoms in a sample to halve

5. What does the activity of a source mean?
The number of decays per second

6. What is the unit of activity?
Becquerel (Bq)

7. What will happen to the number of ‘mother’ nuclei after two half lives?
1xhalf life 2xhalf life
The number of mother nuclei will be ¼ of the original number

8. What will happen to the activity of a source after two half lives?
1xhalf life 2xhalf life
The activity will be ¼ of the original activity