Ohm’s Law

We know that current is the amount of electrons flowing past a point every second and that a force known as the e.m.f. (or voltage) is pushing them. We also know that the conductor will try to oppose the current, by offering a resistance to the flow of electrons.

Ohm’s law, the means by which these three topics (current, voltage, resistance) are linked together, is probably the most important electrical concept that you will need to understand and is stated as follows: the current in a circuit is directly proportional to the voltage applied to the circuit, and indirectly proportional to the resistance of the circuit, provided that the temperature affecting the circuit remains constant.

Ohm’s law was named after the nineteenth-century German physicist Georg Simon Ohm, who researched how current, potential difference and resistance are related to each other.

In simple language we could rewrite Ohm’s law as follows: the amount of electrons passing by every second will depend on how hard we push them, and what obstacles are put in their way. We can prove this is true, because if we increase the voltage (push harder), then we must increase the number of electrons that we can get at the other end. Try flicking a coin along the desk. The harder you flick it, the further it travels along the desk. This is what we mean by directly proportional. If one thing goes up (voltage), then so will the other thing (current).

Equally we could prove that if we increase the resistance (put more obstacles in the way), then this will reduce the amount of electrons that we can get along the wire. This time put an obstacle in front of the coin before you flick it. If flicked at the same strength, it will not go as far as it did before. This is what we mean by indirectly proportional. If one thing goes up (resistance), then the other thing will go down (current).

Ohm’s law can be expressed by the following formula:

Ohm’s law

is a very simple and useful tool for analyzing electric circuits. It is used so often in the study of electricity and electronics that it needs to be committed to memory by the serious student. There is a trick to remembering how to solve for any one quantity if the other two are given. First, arrange the letters V, I, and R in a triangle like this:

 

If you know V and I, and wish to determine R, just eliminate R from the picture and see what is left:

 

If you know V and R, and wish to determine I, eliminate I and see what is left:

 

Lastly, if you know I and R, and wish to determine V, eliminate V and see what is left:

If you are comfortable with algebra, all you need to do is commit V=IR to memory and derive the other two formulas from that when you need them.

 

2. Now read the text once again looking up any word you do not understand in a dictionary and answer the following questions.

1. What is the electric current?

2. What is the electromotive force?

3. What is the resistance?

4. What three topics are linked together in Ohm’s law?

5. What did Georg Simon Ohm research?

6. What example is given in the text to illustrate Ohm’s law?

7. What simple method for remembering Ohm’s law do you know?

 

3. Decide if these statements are true or false. Quote from the text to support your decisions.

1. In the nineteenth century the German physicist Georg Simon Ohm investigated the relationship between current, potential difference and resistance.

2. The resistance of a conductor is a measure of its opposition to the passage of an electric current.

3. According to Ohm’s law the current in a circuit is directly proportional to the resistance of the circuit.

4. From the Ohm’s law formula we can say that the current in a circuit is indirectly proportional to the voltage applied to the circuit.

5. The more the resistance of the circuit, the less the current.

6. The more the voltage, the more the current.

 

Pronounce correctly

 

4. Read the following words with qu:

[kw] question, quote, square, equal, equality, quiz, equipment, quite, quiet, squirrel, quirk, queen, quid, quit, quick, equivalent;

[k] briquette, bisque, toque.

 

5. Read the words given below paying special attention to the ending –ing.

Flowing, pushing, following, affecting, writing, omitting, increasing, travelling, going, flicking, expressing, opposing, offering, referring, resisting, understanding, meaning, forcing.

 

6. Read the words paying attention to the stress l:

 

l Ÿ offer topic increase Simon language obstacle concept student

Ÿ l oppose research increase reduce provide commit arrange

l Ÿ Ÿ probably difference equally following formula analyze memory

Ÿ l Ÿ resistance directly remember determine

 

Increase your vocabulary

 

7. Find these words and word combinations in the text and try to remember them:

 

affect as follows commit to memory determine directly proportional eliminate go down go up indirectly proportional law means

name after obstacle offer resistance to oppose point prove remain research solve for state strength

 

Prefixes say a lot

8. Make new words using the prefix re-that has the meaning do again and translate them.

Example: write – писати rewrite – переписати

Open, read, construct, new, distribute, charge, do, join, consider, appear, sell, pay, apply, number, lay, produce, production, cycle.

 

9. The prefixes in-, il-, im-, ir- give words the opposite meaning. Translate the words given below and use some of them in your own sentences.

Indirectly, invisible, indefinite, inefficiency, illogical, illegal, illiterate, impossible, immovable, impolite, immoderate, imperceptible, irrational, irregularity, irrotational, irreplaceable, irresponsible.

 

10. Match the words in A with the words which have similar meaning in B.

A. Every, to oppose, to link, to state, to mean, following.

B. Next, to resist, each, to imply, to connect, to formulate.

 

11. Match the words in A with their opposites in B.

A. Probable, directly, resistance, simple, true, up, similar, responsible, desirable, remember.

B. Down, conductance, undesirable, irresponsible, improbable, indirectly, false, forget, complex, dissimilar.

 

12. Put other, another, the other into the gaps.

1. Could you give me ____ example? 2. There is only one glove on the table. Where is ____? 3. He has ____ plans. 4. An electron and a proton attract each other because one is positive and ____ is negative. 5. The movement of free electrons from one place to ____ is referred to as current flow. 6. An object, which has gained 6.24 x 10¹⁸ electrons, has a negative charge of one coulomb. On ____ hand, an object, which has given up 6.24 x10¹⁸ electrons, has a positive charge of one coulomb. 7. The battery produces a negative charge at one terminal and a positive charge at ____ end. 8. Conductors are used to carry electricity from one place to ____.

 

Word range

13. Which sentence best illustrates the use of the word in italics taken from the text?

1. We know that current is the amount of electrons flowing past a point every second…

a. A voltmeter measures the potential difference between point A and point B.

b. Could you point a pencil, please?

c. I didn’t understand the point of his joke.

2. There is a trick to remembering how to solve for any one quantity if the other two are given.

a. I prefer quality to quantity.

b. V is a known quantity in this equation.

c. Jack has a very small quantity of English books.

 

Revise your grammar