Electric current

Everything around us is made of “atoms”. They have the nucleus and the electrons orbiting around it. The nucleus is positively charged, and the electrons are negatively charged. Things with opposite charges attract each other, and things with the same charge repel each other. Since electrons are negatively charged, they are attracted to the positive end of a battery and repelled by the negative end.

Some materials let electrical charges flow through them. This creates an electric current. When electrons are flowing through something, you can say that electric current is flowing. Electric current travels very easily through metals like copper, gold, silver, and aluminium. Materials that allow the flow of electrical current through them are called conductors. Since metals are good conductors of electricity, electrical wires are made out of metal. When current flows through a metal, the nucleus of the atoms stay stable, and the electrons move towards the positive end.

Conductors have to be enclosed in a material that is an insulator. Insulators do not allow electric current to pass through them. The rubber coating that you see on electrical cords covers the metal. The electric current stays inside the cord so we can direct the current to the appliance that needs power.

Electric circuits

An electric circuit is a closed loop where current can flow around, electrons pushing other electrons. If you cut the wire you no longer have a complete circuit.

A basic circuit can be composed of a generator, for example a battery; a receiver, such a light bulb; a wire; and control elements, such as a switch or a push-button, as shown in the following figure.

Figura Elementary circuit

Cells and batteries are the source of direct current (DC) to an electrical circuit. They are represented by the symbol in the figure, where we can see the positive (+) and the negative (-) poles.

Switches control the flow of current in a circuit. Switches are binary, which means they can only show one of two possible states: open or closed. An open switch will not allow the flow of current. A closed switch means that the space between the two contacts is ‘closed’ and current can flow freely.

  • Battery symbol/-20
  • Battery symbol

The abbreviations AC and DC are often used to mean simply ‘alternating’ and ‘direct’. Direct current (DC, also dc) is the unidirectional flow of electric charge. It is produced by sources such as batteries or solar cells. The electric charge flows in a constant direction.

  • Switch symbol/10
  • Switch symbol

In alternating current (AC, also ac), the movement of electric charge periodically reverses direction. AC is the form in which electric power is delivered to businesses and residences.

When electrons are flowing through something, you can say that electric current is flowing. But, how do we measure electric current? We use a physical unit called Amper. Ampers are defined referring to the amount of electrons that are flowing per second throughout a conductor material.

One Ampere is equivalent to 6,24·1018 electrons flowing per second.

Electric current

Electric current refers to the amount of electron flow. One amp means that a lot of electrons are flowing. See in the table below some examples of different currents we might encounter in our daily life.

Taula: Examples of different amounts of electric current we might encounter in our daily life
Approximate currentSituation
1 nA - 1 µATiny currents in the receiving antenna of your mobile phone
10 mATV remote control
50 mAKeyboard & mouse
1 AHigh power flashlight
3 ATypical laptop
15 AMicrowave ovens, vacuum cleaners
10,000+ AA bolt of lightning


Bill Sparks is 23 years old. He is from Birmingham, in the UK. He participates in a students’ interchange programme, and he has come to Barcelona to work as an assistant in an electrical company in Barcelona. Today is his first day at work.

Jenny: Hello, sir. How can I help you?

Bill: Hello, I’m Bill, I’m here for the interchange programme.

Jenny: Welcome, Bill! I’m Jenny. Pleased to meet you.

Bill: Thank you. Pleased to meet you too.

Jenny: I would like to introduce you to Jordi, your tutor.

Jenny: Jordi, meet Bill, your new assistant.

Jordi: Hi, Bill. It’s a pleasure to have you here.

Bill: It’s a pleasure for me too.

Jordi: Bill. First, I’ll show you the office and then the equipment and the tools. There is something that will be useful for you. You will have to learn the language, so you can start with this: a list of tools with their names translated into English.

Bill: Thank you, Jordi. It will be really useful for me.


  • Opposite charge: càrrega oposada
  • Same charge: la mateixa càrrega
  • Positive/negative ends: pols positiu/negatiu
  • To flow: fluir
  • Copper: coure
  • Gold: or
  • Silver: plata
  • Electrical wires: cables elèctrics
  • Insulator: aïllant
  • Rubber coating: recobriment de goma
  • Appliance: aparell
  • Loop: bucle
  • Battery: bateria, pila
  • Light bulb: bombeta
  • Switch: commutador/interruptor
  • Push-button: polsador
  • Source of: font de
  • Direct current: corrent continu
  • Alternating current: corrent altern
  • Keyboard: teclat
  • Microwave oven: forn microones
  • Vacuum cleaner: aspiradora
  • A bolt of lightning: un llamp


Pronouns (Cat. pronoms) are very important words in a language. We use pronouns to refer to nouns. For example, when we say: David is here. He is my friend, we use the pronoun ‘he’ to refer to ‘David’. In this way, we do not need to repeat the noun.

In English, the pronouns have different forms when they are the subject (Cat. subjecte) or the object (Cat. complement) of a sentence (Cat. oració).

The elements of an English sentence

A sentence is a group of words that have a meaning. In a sentence, the words have different functions. The most important are:

  • The subject (S): it says who or what does the action of the verb. For example: David is here.
  • The verb (V): it expresses the action or the state of the subject. For example: David is here.

Other common functions are:

  • The direct object (DO): it says who or what receives the action of the verb. For example: David drinks a cup of tea in the evening.
  • The indirect object (IO): it says who or what receives the direct object. For example: David gives his friend a cup of tea.
  • The adverbial of time (AT): it says when the action happens. For example: David drinks a cup of tea in the evening.
  • The adverbial of place (AP): it says where the action happens. For example: David is here.

A basic verb in English is the verb to be (Cat. ser, estar). As all the verbs, the verb to be has different forms. These forms depend on the subject of the sentence. We call the different forms of the verb the conjugation (Cat. conjugació) of that verb.

Subject and object pronouns

Subject pronouns

The subject pronouns always have the function of subject in the sentence. They have the following forms:

Taula: The subject pronouns
Singular Plural
First person: I jo we nosaltres
Second person:you tu, vostè you vosaltres, vostès
Third person: he ell they ells, elles
she ella
it -


  • The first person singular pronoun I (pronounced /ai/) is always written with a capital letter (Cat. majúscula).
  • In English, there is no distinction between the Catalan informal tu and the formal vostè, vostès.
  • The third person singular pronouns he (masculine) and she (feminine) refer to people. The pronoun it (neutre) refers to all the other nouns.

Here are some examples of subject pronouns:

  • I speak English (Cat. [Jo] parlo anglès).
  • You are tired (Cat. ([tu] estàs cansat/da).
  • David is my brother. He works in a hospital (Cat. David és el meu germà. [Ell] treballa a un hospital).
  • Mary is my sister. She lives in Manchester (Cat. Mary és la meva germana. [Ella] viu a Manchester).
  • It is very late. (Cat. - és molt tard).
  • We are at home. (Cat. [Nosaltres] som a casa).
  • How are you? (Cat. Com esteu [vosaltres]?, com estàs [tu]?).
  • These are David and Mary. They are my brother and sister (Cat. Aquests són David i Mary. [Ells]] són el meu germà i la meva germana).

Object pronouns

The object pronouns have the function of object (direct or indirect). We also use the object pronouns after a preposition. The following table shows the forms of the object pronouns and their Catalan equivalent forms:

Taula: The object pronouns
Singular Plural
First person: me me (a mi) us ens (a nosaltres)
Second person:you et (a tu); el, li (a vostè) you us (a vosaltres); els (a vostès)
Third person: him el, li (a ell) them els (a ells, a elles)
she el, li (ella)
it el, la

Examples of the use of the object pronouns:

  • Please help me! (Cat, Si us plau, ajuda’m).
  • David listens to you (Cat. David t‘escolta; David l‘escolta [a vostè]).
  • This is David. Go with him (Cat. Aquest és David. Vés amb ell).
  • This is Mary. Tell her the news (Cat. Aquesta és Mary. Dóna-li la notícia).
  • Mary lives in Manchester. It is a big city (Cat. Mary viu a Manchester. [-] És una gran ciutat).
  • Please come with us! (Cat. Si us plau, vine amb nosaltres!).
  • Are they with you? (Cat. Estan (ells/es) amb vosaltres; estan (/ells/es) amb vostès?).
  • Speak to them! (Cat. Parla amb ells, elles!).

The following text shows the use of pronouns in a text. The pronouns are in bold type (Cat. negreta):

In Catalan and Spanish, we normally omit the subject pronoun. In English, we always write or say the subject pronoun.


David gets up at seven everyday and then he has breakfast. At about eight, he goes to work with Mary, but he does not like going with her because she talks a lot. They usually come back home at five…’


David es lleva a les set cada dia i després (ell) esmorza. Cap a les vui, (ell) va a treballar amb Mary, but a (ell) no li agrada anar amb ella perquè (ella) parla molt. (Ells) normalment tornen a casa a les cinc…’

The verb 'to be'. There is/there are

The verb ‘to be’

The table shows the forms of ‘to be’(in present):

Taula: The verb ‘to be’ (present)
Long form
Short form
Long form
Short form
I am ‘m am not ‘m not am I…?
you are ‘re are not aren’t are you…?
he, she, it is ‘s is not isn’t is he/she/it…?
we are ‘re are not aren’t are we…?
you are ‘re are not aren’t are you…?
they are ‘re are not aren’t are they…?

Long and short forms

Verbs usually have two forms:

  • Long forms: they are used in the written, formal language.
  • Short forms: we omit some letters. They are used in the oral, informal language.

The verb ‘to be’ is used in different ways:

1) As a lexical verb (Cat. verb lèxic), with the meaning of Cat. ser, estar. For example:

  • David is a doctor (Cat. David és metge)
  • He is tired (Cat. està cansat)

2) As an auxiliary verb (Cat. verb auxiliar):

  • To form the continuous tenses of the verbs. For example: David is working now (Cat. David està treballant en aquest moment).
  • To form the passive voice. For example: This is explained in this letter (Cat. Això està explicat en aquesta carta).

The lexical verbs and the auxiliary verbs

The lexical verbs are the verbs that express an action or a state. Practically all the verbs are lexical. The auxiliary verbs are the verbs that we use to form other verb tenses. In English, there are three auxiliary verbs:

  • To be: it forms the continuous tenses and the passive voice.
  • To have: it forms the perfect forms.
  • To do: it forms the negative and interrogative forms of the lexical verbs.

There is / There are

The forms there is (singular) and there are (plural) express the existence of a noun. It is equivalent to Cat. hi ha and Sp. hay. In English, there are two forms: one for the singular and one for the plural, but in Catalan and Spanish, there is only one. Here are all the forms in English:

  • Affirmative: there is…, there are…
  • Negative: there is not … there are not …
  • Interrogative: is there…?, are there…?


  • There is a person at the door (Cat. Hi ha una persona a la porta).
  • There are two people at the door (Cat. Hi ha dues persones a la porta).
  • There is not anything to say (Cat. No hi ha res a dir).
  • There are not many people in the room (Cat. No hi ha molta gent a la sala).
  • Is there anyone in the office? (Cat. Hi ha algú a l’oficina?).
  • Are there any jobs available (Cat. Hi ha feines disponibles?).


In English, there is a great difference between the formal and the informal language. We use the formal language to speak to our superiors at work or to a person that we do not know; we use the informal language to speak to friends, colleagues and family members. The English give a lot of importance to formalities, so we must be careful and use the appropriate language in each situation.

There are four skills (Cat. habilitats) in all the languages:

See Unit 1, section 2 ‘Communication’ for learning about the written skills

  • Oral skills: listening and speaking
  • Written skills: reading and writing

Learning a foreign language means to develop the four skills. For this, you need a lot a lot of practice: you must speak English to speak fluently; you must listen to English understand the language; you must write to produce an accurate text and you must read to understand a written text.

Formal and informal style

Both styles are correct; it is only a matter of tone and setting. These are the main characteristics of the formal and the informal styles:

See annex ‘Formal and informal style’ for examples of the two styles in business letters.

Formal style:

  • It uses the long forms of the verbs verbs: I am, he is not, etc.
  • It uses the full forms of the nouns, and not the abbreviations: photograph (and not: photo), television (and not: TV), etc.
  • In requests, it uses the form could you…?, and not the imperative form: could you help me? (and not: help me!).
  • It frequently uses the passive voice, especially in written English: it is considered that… (and not: people consider that…), etc.
  • It uses the formal versions of words and expressions: post (and not: job), I would like… (and not: I want…), etc.
  • In writing, it uses longer, more complex sentences.

Informal style:

  • It uses the short forms of the verbs. For example: I’m, he isn’t, etc.
  • It generally uses the abbreviated forms of the nouns. For example: photo, TV, etc.
  • In requests, it generally uses the form can you…? or the imperative form. For example: can you help me?, help me!, etc.
  • It does not frequently use the passive voice.
  • It uses colloquial words and expressions: job (for: post), dad (for: father), hi (for: hello), etc.
  • In writing, it generally uses short and simple sentences.

When you write or speak in English, you must be consistent: do not mix the formal and the informal styles. Compare these two texts with the same information, but different language styles:

Formal text

Dear Sir or Madam

This is to inform you that I am interested in the post of administrative assistant advertised in ‘The Guardian’ of 3r March. I would appreciate it if you could send me further details. Thank you in advance.

Yours sincerely

Informal text


Do you remember the advertisement for a job as an administrative assistant? It was in ‘The Guardian’ of the last 3rd March. Well, I inform you that I’m interested in this job. Can you tell me more about it? Thanks.


The listening skills

Like all the skills, the only way of developing your listening skills is by practising as much as you can. You must train your ear to the sounds of the English language, so you must listen to people speaking in English. The best option is to practise with another person (preferably a native speaker). If you have no possibility of speaking in English, there are other options for practising the listening skills. Here is a list of options:

Check the ‘Interesting links’ section in the course material for a list of websites with listening activities.

  • Watch films, TV series or TV documentaries in their original language (most are in English). Of these, documentaries are the easiest to understand because the speech is more formal and does not include conversations. Use subtitles in Spanish to help you understand, if you wish.
  • Listen to songs in English and read the lyrics at the same time. Do not worry about the meaning of the words; just listen to the sounds and enjoy the music.
  • Watch videos of your interest in YouTube, Vimeo, etc. There are thousands of videos especially created for practising the English listening skills.
  • Surf the Internet. You will find many websites with listening texts, usually with exercises to check your comprehension.

Here is some advice if you decide to practise your listening skills:

  • Do not try to understand all the words that you hear. You must learn gradually: at first, you will understand very little; later on, you will understand more and more things.
  • Be patient. It can take a long time to see the results of your practice: this depends on your previous experience, on the frequency of your practice, on your natural dispositions, on the people’s accent, etc.
  • Do not abandon. You must continue learning after the end of the course, or you may lose the listening skills that you have gained with your practice.

The speaking skills

See annex ‘The Phonetic Alphabet’ for a list of the sounds of the English language.

For many students, speaking is the most difficult of the four skills. Speaking usually happens in two situations:

  • A speech (Cat. discurs, xerrada): for example, in a presentation. In a speech, you speak and other people listen; the language style is usually formal.
  • A conversation (Cat. conversa): it is the most common situation at work and in your daily life. In a conversation, there is interaction with other people; the language may be formal or informal, depending on the situation.

To develop the speaking skills, you must practise a lot. Here is some advice for you:

Check the ‘Interesting links’ section in the course material for a list of websites to practise your pronunciation and speaking skills.

  • To practise your pronunciation, check websites where you can listen to words and sentences; then repeat what you hear. Many online dictionaries (like ‘Wordreference.com’) offer the pronunciation.
  • Find another person to speak to: you can practise with another learner of English or with a native speaker.
  • Check the Internet: some websites offer speaking practice via Skype to students of English from all over the world.
  • Do not be afraid of making mistakes: people will understand that you are not a native speaker.

During a conversation, we can use some common expressions. Here are some examples (with equivalent expressions in Catalan):

To start a conversation:

  • Hello! (informal) (Cat. Hola!)
  • Excuse me (formal) (Cat. Perdoni)

To ask people to repeat:

  • Pardon? (informal) (Cat. Perdoni?)
  • Can you repeat please? (informal) (Cat. Pots repetir si us plau?)
  • Could you repeat please? (formal) (Cat. Podria repetir si us plau?)
  • Could you say that again please? (formal) (Cat. M’ho podria tornar a dir si us plau?)
  • Sorry, but I didn’t understand. What did you say? (formal) (Cat. Perdoni, però no l’he entès. Què ha dit?)

To finish a conversation:

  • Well, I must go I’m afraid (formal/informal) (Cat. Bé, hauria d’anar marxant)
  • OK, it was a pleasure talking to you (formal) (Cat. Bé, ha estat un plaer)
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