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1. DENSITY Clicking here will move you to the next page. BUTTONS Click us: Clicking here will allow you to hear some information on the topic. Clicking here again will stop the sound. Clicking here will move you back a page. Clicking here will reveal some information. Clicking on me will take you to a list of equations, clicking on me again will take you back to the previous page. Clicking here will reveal an answer. TOPICS Clicking here will bring you back to this page. … density and molecules (2 pages). … the equation. … how to measure density. Clicking on me will take you to SI multipliers table. Clicking on me again will return you to your previous page. … practice questions (4 pages) …exam questions (3 pages).

2. DENSITY Density measures how much substance has been squeezed into a particular volume. For the samemass, a a substance with a smallervolume has a greaterdensity. When a substance changes state, the mass doesn’t change but the density changes as the volume changes. Click the ebuttons below to see how this happens at an atomic level. Each diagram contains 16 atoms. LIQUID GAS SOLID

3. DENSITY EQUATION The properties of density, mass and volume come together in the density equation. This shows that the density, , is equal to the mass, m, divided by the volume, V.(We use the Greek letter rho,  , as the symbol of density). Mass in kilograms, kg Density in kilograms per cubic metre kg/m3 Units 1 Volume in cubic metres, m3 Density of water = 1000 kg/m3 Densit of air = 1.2 kg/m3 mV mV Mass in grams, g Density in grams per cubic centimetre g/cm3   = = Units 2 Volume in cubic centimetre, cm3 Density of water = 1 g/cm3 Density of air = 0.0012 g/cm3

4. DENSITY OF ICE and WATER Ice floats on water because ice is lessdense than water. The ice molecules leave smallgaps in the pattern which increases the volume of ice. The water molecules are closer together which produces a smallervolume and so a largerdensity. mV  = ICE WATER

5. DENSITY OF A REGULAR SOLID MEASURING MASS MEASURING VOLUME Depth = 4cm Height = 4cm Mas = 600g Cyfaint = 64cm3 màs cyfaint massvolume Volume = height x width x depth = 4cm x 4cm x 4cm Volume = 64 cm3 density= dwysedd = mV  = mV  Width = 4cm = 600g 64cm3 = 600 g 64cm3 CALCULATING DENSITY = 400 600 density,  = 9.4 g/cm3 dwysedd,  = 9.4 g/cm3 800 200 Mass = 600g g 1000 0

6. DENSITY OF AN IRREGULAR SOLID MEASURING MASS MEASURING VOLUME Volume of water = 25 cm3 Volume of water + object = 49 cm3 Volume of object = 49 – 25 cm3 = 24 cm3 massvolume density= 50 CALCULATING DENSITY mV  = 40 200g24cm3 = 30 120 80 density,  = 8.3 g/cm3 20 40 160 10 Mass = 200g g 200 0

7. DENSITY OF A LIQUID We use a volume of 50 cm3 of water in this case. Volume = 50 cm3 MEASURING MASS Mass of measuring cylinder = 100 g Mass of measuring cylinder + water = 150 g Mass of water = 150g – 100g = 50 g 50 40 CALCULATING DENSITY massvolume density= 30 150 100  mV = 20 50g 50cm3 200 50 = 10 density,  = 1.0 g/cm3 g 250 0

8. PRACTICE QUESTION 1 Use the density equation to find the following materials. You have found an old penny when digging in the garden. Its mass is 26.8 g and volume 3 cm3 A lost ring has turned up of mass 107 g. After filling a measuring cylinder with 10 cm3 of water and then adding the ring, the level rises to 15 cm3 . density = mass= 26.8 g = 8.93 g/cm3 volume 3 cm3 What is the penny made from? copper volume = 15 cm3 —10 cm3 = 5 cm3 You have a paperweight on you rdesk which measures 3 cm by 4 cm by 6 cm.Its mass is 184 g. density = mass= 107 g volume 5 cm3 = 21.4 g/cm3 volume = 3cm x 4cm x 6cm = 72cm3 density = mass= 184 g = 2.56 g/cm3 volume 72 cm3 What is the ring made from? platinum What is the material? marble

9. PRACTICE QUESTION 2 A pupil is experimenting with three unknown liquids and obtains the following results: Liquid A: mass = 2060 grams, volume = 2000 cm3 Liquid B: mass = 672 grams, volume = 850 cm3 Liquid C: mass = 990 grams, volume = 1100 cm3 How would the 3 liquids appear as layers if added carefully together in the 5 litre beaker? B Density A = mass= 2060 g = 1.03 g/cm3 volume 2000 cm3 C You need to calculate their densities first. Density B = mass= 672 g = 0.79 g/cm3 volume 850 cm3 A Density C = mass= 990 g = 0.90 g/cm3 volume 1100 cm3 A less dense liquid will float on a more dense liquid. Liquid B is the least dense and so floats on the other two.

10. EXAM QUESTION 1 Mass of oil = 102 – 74 = 28 g 152 – 102 = 50 g Mass of water =

11. WJEC: Physics 1 June 2016 (Found.) Q.6 (High) Q.1 28 50 50 density = mass= 28 g = 0.80 g/cm3 volume 35 cm3 REMEMBER: EQUATION NUMBER ANSWER UNIT

12. EXAM QUESTION 2 - Higher WJEC: Physics 1 Jan 2016 (Higher) Q.6 24 turbines Volume of water from one turbine = 700 m3 per second (in table) Max volume of water from the barrage = 700 x 24 = 16,800m3/s  = m m =  x V = 1000 x 16,800 = 1.68 x 107 kg/s V REMEMBER: EQUATION REARRANGE NUMBERS ANSWER UNIT

13. EXAM QUESTION 2 Maximum power = 24 x 10 MW = 240 MW You can use 240,000,000 watt and 3,500 volts here. P = V x I I = P = 240 MW = 240 x 106 = 6.86 x 104 = 68.6 kA V 3.5 kV 3.5 x 103 Mae’r cwestiwn yn gofyn am gerrynt a’r tabl yn rhoi pŵer a foltedd. Felly hafaliad sy’n cysylltu y tri yw’r un i ddewis., 68,600 % efficiency = useful power output x 100% total power input = 10 MW x 100% = 62.5% 16 MW 62.5% As both values are in megawatts there is no need to change them.

14. EQUATIONS higher higher Open the file “Maths for Physics” for more about the use of mathematics in Physics.

15. SI MULTIPLIERS k - kilo p - pico n - nano M - mega G - giga  - micro m - milli T - tera You only see the letter of the prefix on an exam paper, NOT the name. On a Foundation paper only milli, kilo a mega are used.