Transcript P2.4_-_Charge,_potential_difference,_ene... 307KB Jun 06 2014 10

Charge, potential
difference, energy
and current
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What does it mean if something is described as charged? the object has a
net positive or negative charge due to electrons being taken away or given to
the object (2 marks)
List 3 ways that static electricity is used in industry? Any three from:
Electrostatic precipitator (smoke scrubbers in chimneys). Photocopiers.
Printers. Powder coating/spraying. (3 marks)
For one of the above examples, describe how the process works.
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What is the equation that links charge, current and time? Q = It
...................................................(1mark)
What is the equation that links charge, potential difference and energy?
E = QV................................(1 mark)
How much charge flows when a current of 2A flows for 30 seconds?
..............................60C........................(1mark)
What current flows if a charge of 300C flows for 3minutes?
……………………1.7A....................................(1 mark)
What current flows if a charge of 270C flows for 106seconds?
…………………2.5A…………………………………….(1 mark)
A p.d. of 12V is applied across a resistor. 250C of charge passes. How much
energy was dissipated by the resistor ?
…...............................3000J.........................................(1 mark)
A current of 0.12A flows through a resistor which has a resistance of 150
Ohms, 300C of charge passes. How much energy was dissipated by the
resistor? V = IR V = 18..18x300 = 5400J.............................(2 marks)
A light bulb releases 230J of energy when connected to a 11V battery. How
much charge flowed in the circuit?
…………………20.9C………………………………….……(1 mark)
The diagram shows a charged thundercloud.
(a) Why does the tree below the thundercloud become positively
charged?
electrons / negative charges are
Repelled
(1 mark)
(b) The base of the cloud has a negative charge of 18 coulombs.
The potential difference between the base of the cloud and the
ground is 1 200 000 kilovolts.
(i) Write down the equation that links charge, energy transferred
and potential difference.
energy (transferred) = potential
difference × charge
(accept E = V × Q, accept W = V × Q)
(1 mark)
(ii) Calculate the maximum energy that could be transferred to the
ground by a lightning
strike. Show clearly how you work out your answer.
......E = VQ = 1200000 x 18 = 21600000000..........
Maximum energy transferred =21 600 000 000 or 2.16 × 1010
joules
(2 marks)
(c) A lightning conductor is usually attached to tall buildings. This
reduces the risk of damage by a lightning strike.
Explain why the lightning conductor is made of copper.
copper is a good (electrical)
conductor or copper has a low
Resistance (1 mark)
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provides path for electrons /
electricity / lightning to earth /
ground / metal plate (1 mark)