Potential Difference

Question 1

What is potential difference? (Formula)

Answer 1

V=W/Q (Where V is the voltage/potential difference, W is the work/energy and Q is the charge)

Question 2

What is potential difference? (Definition)

Answer 2

The potential difference, or voltage, between two points in an electric field is the work required to move a charge of 1C from one point to the other.

Question 3

Define the Volt.

Answer 3

The volt can be defined as the potential difference between two points, if 1J of work is required to move 1C from one point to the other.

Question 4

What is the term used to describe the potential difference of charges that are large distances apart?

Answer 4

Zero potential. (This can also be said of any charge connected to the Earth)

Question 5

What does emf stand for?

Answer 5

Electromotive force. (It differs form potential difference as pd is energy supplied to each part of the circuit, while emf is voltage generated by the battery.)

Question 6

Describe what a primary cell is composed of and give an example of it. (Also known as galvaonic/voltaic cell.)

Answer 6

• Two different electrodes/metal plates (eg. zinc & copper) in electrolyte/ionic solution (eg. sulphuric acid)
• Zinc releases positive ions
• Copper releases negative ions
• If potential difference is applies across the cell, current flows
• It cannot be recharged
• An example is a household battery

Question 7

Describe what a dry cell is composed of and give an example of it.

Answer 7

• Two electrodes (zinc and carbon)
• Paste electrolyte (manganese dioxide)
• One eletrode forms the positive cap (carbon rod)
• The other forms the negative base (zinc can)
• Cannot be recharged
• An example is an alkaline battery

Question 8

Describe what a secondary cell is composed of and give an example of it. (Also known as an accumulator.)

Answer 8

• The electrodes are lead plates
• Sulphuric acid is the electrolyte
• Can be recharged (this is done by reversing the current)
• Examples are lithium ion batteries in phones and car batteries

Question 9

Other than the three types of cells, (primary, secondary and dry) give a source of emf used in the home.

Answer 9

Mains electricity. (This is alternating cylce electricity, produced by an oxillating coil/magnet.)

Question 10

Explain how a thermocouple works as a source of emf.

Answer 10

• Two metals are joined at a hot and a cold junction
• The temperature difference produces an emf proportional to the temperature difference

Question 11

What way does voltage behave in series? (What does total voltage equal?)

Answer 11

V_Total = V₁ + V₂ + V₃

Question 12

What way does voltage behave in parallel? (What does total voltage equal?)

Answer 12

V_T = V₁ = V₂ = V₃

(To note: when in parallel, bulbs will be brighter, but the battery will be used up quicker.)

Question 13

Derive P=VI

Answer 13

From V=W/Q we get,

W=VQ

Divide both sides by t:

W/t=(VQ)/t

But P=W/t & I=Q/t

Therefore P=VI

Question 14

Why must voltmeters be placed in parallel when measuring voltage?

Answer 14

This must be done because they have resistance, and if they were to be put in series, their resistance would affect the results. Voltage in parallel is equal, and so it can be measured by a voltmeter that’s in parallel.