E L E C T R I C I T Y

YEAR 9 SCIENCE

TEACHER CONTACTS

• Mrs Schoenmaker• Location: Science Staffroom E05

TOPICS THIS YEAR

• Electricity• Life through the Ages• Coordination and Control• The Restless Earth• Chemical reactions• Ecology• The Universe

ELECTRICITY – UNIT OVERVIEW

• In this unit we examine the electrical world. • Electricity as a most

common source of energy• It is invisible, clean

and quiet. Yet, it can give you a shock or kill you!

LUIGI GALVANI

In 1791, was an early scientist to experiment with electricity

Frogs – he wrongly hypothesized that animal electricity was produced when frogs touched to different metals

FROG EXPERIMENT

VOLTA

In 1800 he explained that a chemical reaction occurs between two different metals in contact with a moist material.

This reaction generates an electric current

He also made the first electro-chemical cell

ELECTROCHEMICAL CELL

WHAT IS AN ELECTROCHEMICAL CELL?

• An electrochemical cell is a device used for generating an electromotive force (voltage) and current from chemical reactions, or the reverse, inducing a chemical reaction by a flow of current. The current is caused by the reactions releasing and accepting electrons at the different ends of a conductor. A common example of an electrochemical cell is a standard 1.5-volt battery. Batteries are composed of usually multiple Galvanic cells.

YOUTUBE CLIP

• http://www.youtube.com/watch?v=0oSqPDD2rMA• http://www.youtube.com/watch?v=nNG5PMlHSoAHEADING: Timeline of Electricity

HISTORY OF ELECTRICITY• http://www.youtube.com/watch?v=P0ggjtK0Ddo&f

eature=related• http://www.youtube.com/watch?v=Sk1P8r2xm5I&

feature=related• http://www.youtube.com/watch?v=IpaEGhjpZgc&f

eature=related

OHM’S LAWS

• Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship

• http://www.youtube.com/watch?v=QwNSa_8ro_Y

TODAY

• Copy and complete (CCs)• Questions 1-6• Q1 – Timeline (Make this using 1 whole page)

COPY AND COMPLETE

• Our understanding of electricity has developed slowly. Through experiments and discoveries people learnt new knowledge. This allowed them to do further experiments and to learn and understand even more. Our knowledge of electricity comes from the contribution of many people.

•  • There is still much more to be invented and discovered.

Better solar cells are needed to obtain the energy from sunlight. Electric cars are not yet practical because there are no batteries that can store enough electrical energy. Super conductors will revolutionise the electrical and electronic devices of the future.

ANSWERS

1. Draw a time line from the discovery of current electricity to the present day. Mark on it the major inventions and discoveries described in the text. 

1791 Galvani observed twitching of frog’s legs.1800 Volta reported chemical reactions can cause electricity.1820s Oersted linked electricity and magnetism.

Ampere’s mathematics connected electricity and magnetismOhm’s law. 1831 Faraday and Henry made electricity from magnetism.(Subsequently, Faraday discovered electrolysis.)1864 Maxwell’s equations linked electricity and magnetism and he predicted electromagnetic waves.1876 Bell invented the telephone.1877 (and 1879) Edison invented the record player and electric light bulb.1890s Vacuum tubes first made.

ANSWERS

1891 Storey explained the nature of electricity.1895 Marconi broadcast the first radio message.1897 Thomson proved the existence of electrons.1947 Transistors were invented.  3. Most discoveries in science are now achieved by teams of scientists working together. Give two examples of this from the text. (i) In the 1890s, teams of scientists made vacuum tubes. (ii) Transistors were invented in 1947 by a team of American physicists.

ANSWERS

 4. Give two examples from the text where a discovery has resulted from an observation. Two examples are:(i) Galvani’s observations of the effect of two different metals on frog’s legs were followed soon after by Volta’s discovery of the electrochemical cell. (ii) Oersted’s observations of the movement of compass needles were followed soon after by Ampere’s discovery of the mathematical connection between electricity and magnetism. 5. Sometimes a new theory is proposed and later discoveries can support or reject it. Explain how radio broadcasting began with an unproven theory and prediction. James Clerk Maxwell had predicted the existence of electromagnetic waves, but it was, at the time, an unproven idea. However, Hertz then produced such waves and, soon after, Marconi used Hertz’s discovery to broadcast the first radio message.

ANSWERS

 6. Many discoveries about electricity were made in Europe by men. Suggest some historical reasons for this. Some possible reasons are: (i) In the 18th and 19th centuries, women were not, for social reasons, expected to pursue professional careers. (ii) In the 18th and 19th centuries, the study of science was for boys and science careers were for men (the concept of females studying science and then becoming scientists was almost unthinkable in that era). (iii) Europe was the ‘seat of learning’ in the Old World at that time. The New World had barely begun.•  •  •  •