Y12 assessment mark scheme

6732 Unit Test PHY2 June 2004 (electricity only)

1. Charge

Charge is the current x time ü ( Where you see this symbol there is supposed to be a tick) 1

Potential difference

Work done per unit charge [flowing] ü 1

Energy

9V x 20C ü

=180J ü 2

Total 4

2. Number of electrons

(-64 x 10^-9C)/(-1.6 x 10^-19 C) = 4.0 x 10¹¹ electrons

Use of n = Q/e ü

Seeing 1.6 x 10^-19 C ü

Answer of 4.0 x 10¹¹ (electrons) ü 3

[Use of a unit is a ue] [-ve answer: 2/3]

Rate of flow

(6.4 x 10-⁸ C)/3.8 s = 16.8/17 [uC s-¹] OR 16.8/17 x 10-⁹ [C s-¹]

(6.4) / 3.8 s i.e. use of I = Q / t [Ignore powers of 10] ü

Correct answer [No e.c.f] [1.7 or 1.68 x 10-⁸ or 1.6 x 10^-8 ü 2

Unit

Amp(ere)/A ü 1

Total 6

6 Explanation of observation

Any two from:

• LED on reverse bias/R in LED infinite/ LED wrong way round
• so current is zero /LED does not conduct / very small reverse bias current
• since V = IR.
• V=0x1K=0V üü

Explanation of dimness

Rv very large / R_v much greater than RLED

Current very low / pd across LED very small (not zero) üü 2

Circuit diagram

LED in forward bias ü

Variation of pd across LED ü

Voltmeter in parallel with LED alone ü 3

(LED in series with voltmeter 0/3]

total 7

7. Circuit diagram

Ammeter in series with cell and variable resistor (correct symbol) ü

Voltmeter in parallel with cell OR variable resistor ü 2

Power output at point X

Power = voltage x current ü

=0.45V x 0.6A

= 0.27 W ü 2

Description of power output

Any three from:

Current zero; power output zero/small/low

• As current increases power output also increases

• Then (after X ) power decreases

• Maximum current; power output zero ü ü ü 3

[Accept reverse order]

e.m.f. of cell

0.58 V ü 1

Internal resistance

Attempt to use " lost volts" OR E = V + IR current ü

_ 0.58V-0.45V 0.6 A

= 0.217 / 0.2 ohm ü 2

[ecf an emf greater than 0.45 V]

Total 10

8 Statement 1

Statement is false ü

Wires in series have same current ü

Use of I = nAev with n and e constant ü

[The latter two marks are independent] 3

Statement 2

Statement is true ü

Resistors in parallel have same p.d. ü

Use of Power = V²/R leading to R inc, power dec ü

OR as R inc I dec leading to a lower value of VI

3^rd mark consequent on second 3

total 6

Year 9 Global Warming

Global Warming

The Earth receives a constant supply of energy from the sun which is 150 million km away in the form of electromagnetic radiation. We can measure the amount of energy we receive from the sun and use that to calculate what the average surface temperature of the Earth should be. Surprisingly this gives an answer of –17C. We measure the average temperature to be +9C. What’s wrong.
Actually nothing. It’s the greenhouse effect that increases our temperature.

What is the greenhouse effect?

The surface of the sun is about 6000C. This means the em rays have a short wavelength. They heat the earth up. The Earth at 9C is much hotter than space so it also gives out radiation. The Earths em rays have a longer wavelength than the sun’s.

The Greenhouse gases
Carbon Dioxide, Water Vapour, Methane

The short waves from the sun do not interact with the molecules of these compounds, but the longer waves emitted by the Earth’s surface hit these molecules and make them vibrate. This makes them unstable so after a short while they re emit a low wavelength infra red ray. Some of these head back to Earth. So the Earth loses less heat than it should do. (This is correct; heat is not reflected back from the greenhouse gases)

We wouldn’t be here without the greenhouse effect so what’s the problem?

This graph shows the increase in CO2 since the industrial revolution. Next to it is a graph of the average temperature of the Earth over the same period.



Should we worry?
The Earth’s climate is unstable and has varied much in the recent past. We are at present in an Interglacial period.

It is possible that the present rise is linked to this. Recent studies however suggest that an increase in CO2 is causing an increase in global average temperatures.

Climate change for whatever reason could be disastrous for our current civilisation. Melting polar ice caps could trigger sea level rise. Bizarrely it could make the UK much colder. Changing rainfall patterns could affect global crop production and industrial processes require vast amounts of water.
The effects of a hotter planet would affect the natural world, but the Earth has been much hotter in the distant past and there is evidence that it froze over completely at least once in its history.

Questions.

What is the Earth’s major source of energy?
What should the Earth’s surface temperature be? Why is the greenhouse effect good?
What are the three major greenhouse gases and where do they come from?
Draw a diagram of the earth. Draw in the atmosphere. Show the waves from the sun and earth. Add on the re radiated infra red to show the greenhouse effect.
Why do people worry about CO2 in the atmosphere?
Has the Earth’s climate been stable in the past?
Why do some people feel that the CO2 we release into the atmosphere is nothing to worry about and global warming has other causes?
Why do people worry about climate change?
What, if anything, can you do?What should our government do?

Answers to Y12 Hw on Base Units

Watt kg m2 s-3 (Power=Work/time)

Hz s-1

Coulomb As

Ohm kg m2 s-3 A-2

Volt kg m2 s-3 A-1

Apologies for the formatting

This homework is now closed

Y12 Assessment

This will take place on
Thusday 23rd February, period 3
Topics covered Electricity

Y13 Assessment

This will take place on
Wednesday 22nd February Period 5
Topics covered Electric Fields and Capacitors, Magnetic Fields.