Charge and Current What is Charge Nobody really

Charge and Current

What is Charge? • Nobody really knows!

But we do know that… • It comes in two types, which we call positive and negative • Similar charges repel; opposite charges attract • Charge is ‘carried’ by electrons (negative) and protons (positive) • Although a proton is much bigger than an electron, they both carry the same amount of charge (but opposite)

Atoms

Atoms (negative) (positive)

You can’t have these on their own – they are all carried by other things: • Charge • Beauty • Confidence • Momentum • possessed by electrons and protons • possessed by people, paintings, ornaments, flowers, etc. • possessed by people • possessed by objects

Beauty • Carried by people • Measured in Helens • Takes a lot of people (about 1000 ordinary women!) to carry one Helen of beauty between them Charge • Carried by electrons and protons • Measured in coulombs • Takes a lot of electrons (about 6, 200, 000, 000!) to carry one Coulomb of charge between them

It takes many women to make a Helen… x 10 1 thousandth of a Helen (1 m. H) makes up 1 Helen (1 H)

It takes many electrons to make a coulomb… e 0. 00000000016 of a Coulomb x a gazillion (or so) makes up one Coulomb

i. e. • One coulomb of electric charge is one GREAT, BIG, HONKING quantity of charge, • while one electron carries a pathetically minute quantity of charge.

Typical Amounts of Charge • When you rub a balloon against your hair, you build up around a trillionth of a coulomb of unbalanced charge on the balloon (and on your hair). The balloon has gained around one extra electron for every ten trillion it had already. • The Van de Graaff generator contains more unbalanced charge: around 0. 00005 C. • About 20 C of charge are transferred in a lightning strike.

Neutral Matter • A cubic centimetre of copper contains a total of about 750, 000 C of charge altogether (half negative – in electrons; half positive – in protons). • About 13, 000 C of this is carried by free electrons.

Charge Questions 1. We don’t really know what charge actually is – but what do we know about it? 2. What are the tiny particles that carry charge? Which is positive and which is negative? Where are they each found? 3. What is the unit of charge (give the full word and also the symbol)? 4. Copy and use your own more interesting adjectives to fill in the gaps: The amount of charge in a coulomb is ______ [very large]. The amount of charge on an electron is ______ [very small]. 5. Add your own illustrations to this piece of work (optional).

Current • Current is the rate of flow of charge (i. e. how much charge is flowing past per second) • Animation: flowing electrons • Animation: electrons in a circuit • So current is measured in Coulombs per second (C/s) • BUT the C/s has its own particular name: the ampère, amp, or A.

Moving Electrons • When electrons carry charge along a wire, they move slower than the minute hand on a clock. • Animation: free electrons flowing

Relationship between Charge, Current and Time • Write a little three-word formula showing the relationship between these three quantities. Charge = current x time (in C) (in A) (in s) Q I t

Example questions on current Charge (C) Current (A) Time (s) 5 2 0. 4 1 20 0. 5 50 250 3 60 1) A circuit is switched on for 30 s with a current of 3 A. How much charge flowed? 2) During electrolysis 6 A was passed through some copper chloride and a charge of 1200 C flowed. How long was the experiment on for? 3) A bed lamp is switched on for 10 minutes. It works on a current of 0. 5 A. How much charge flowed?

Example questions on current Charge (C) Current (A) Time (s) 10 5 2 0. 4 1 0. 4 20 0. 5 40 50 0. 2 250 180 3 60 1) A circuit is switched on for 30 s with a current of 3 A. How much charge flowed? 2) During electrolysis 6 A was passed through some copper chloride and a charge of 1200 C flowed. How long was the experiment on for? 3) A bed lamp is switched on for 10 minutes. It works on a current of 0. 5 A. How much charge flowed?

Example questions on current Charge (C) Current (A) Time (s) 10 5 2 0. 4 1 0. 4 20 0. 5 40 50 0. 2 250 180 3 60 1) A circuit is switched on for 30 s with a current of 3 A. How much charge flowed? Q = I x t = 3 x 30 = 90 C 2) During electrolysis 6 A was passed through some copper chloride and a charge of 1200 C flowed. How long was the experiment on for? 3) A bed lamp is switched on for 10 minutes. It works on a current of 0. 5 A. How much charge flowed?

Example questions on current Charge (C) Current (A) Time (s) 10 5 2 0. 4 1 0. 4 20 0. 5 40 50 0. 2 250 180 3 60 1) A circuit is switched on for 30 s with a current of 3 A. How much charge flowed? Q = I x t = 3 x 30 = 90 C 2) During electrolysis 6 A was passed through some copper chloride and a charge of 1200 C flowed. How long was the experiment on for? t = Q / I = 1200 / 6 = 200 s 3) A bed lamp is switched on for 10 minutes. It works on a current of 0. 5 A. How much charge flowed?

Example questions on current Charge (C) Current (A) Time (s) 10 5 2 0. 4 1 0. 4 20 0. 5 40 50 0. 2 250 180 3 60 1) A circuit is switched on for 30 s with a current of 3 A. How much charge flowed? Q = I x t = 3 x 30 = 90 C 2) During electrolysis 6 A was passed through some copper chloride and a charge of 1200 C flowed. How long was the experiment on for? t = Q / I = 1200 / 6 = 200 s 3) A bed lamp is switched on for 10 minutes. It works on a current of 0. 5 A. How much charge flowed? Q = I x t = 0. 5 x 600 = 300 C

Current Practical 1. Use the bulbs, leads and cells to build a simple series circuit. Draw the circuit diagram in your book. Measure the current. (Where should you put the ammeter? ) Mark the current(s) on your diagram. 2. Use the equipment to answer the following questions: If you have a fixed number of cells of a particular voltage each, do they always give exactly the same current or can you make the current more or less? Draw diagrams of the circuits you make. Mark the current(s) on your diagrams.

Reminder: how to draw circuit diagrams

Reminder: how to draw component symbols Cell

One day you might be designing your own guitar amps…