Lecture 60 – Lecture 61 Producing Electric Current Ozgur Unal NIS – PHYSICAL SCIENCE Lecture 60 – Lecture 61 Producing Electric Current Ozgur Unal

From Mechanical to Electrical Energy In 1831, Michael Faraday and Joseph Henry independently found that: moving a loop of wire through a magnetic field causes an electric current to flow in the wire. moving a magnet through a loop of wire produces a current. In both cases, the mechanical energy is converted into electrical energy. The generation of a current by a changing magnetic field is electromagnetic induction. http://www.wainet.ne.jp/~yuasa/flash/EngLenz_law.swf http://micro.magnet.fsu.edu/electromag/java/faraday2/ http://www.educypedia.be/electronics/javamagnetics.htm http://new.wvic.com/index.php?option=com_content&task=view&id=9&Itemid=46

Generators Most of the electrical energy you use every day is provided by generators. A generator uses electromagnetic induction to transform mechanical energy into electrical energy. Check out Figure 17 carefully!

The Electromagnetic Force There is a relationship between electricity and magnetism A changing magnetic field can cause electric charges to move. A moving charge produces a magnetic field. This connection occurs because the electric force and the magnetic force are two different aspects of the same force  electromagnetic force An electromagnetic force exists between all objects that have electric charge. Like electric and magnetic forces, the electromagnetic force can be attractive of repulsive.

Generating Electricity for Your Home Do you have a generator in your home? Electrical energy in your home comes from a power plant with huge generators. The coils in these generators have many coils of wire wrapped around huge iron cores. The rotating magnets are connected to a turbine, which is a large wheel that rotates when pushed by water, wind or steam.

Generating Electricity for Your Home How many types of power plants can you name? Power plants can use: wind, water, fossil fuels, nuclear energy .... to generate mechanical energy Check out Figure 20 to compare generators and electric motors.

Direct and Alternating Current There are two kinds of current flow in a circuit: Direct Current (DC) and Alternating Current (AC) A battery produces a direct current. Direct current flows only in one direction through a wire. http://www.koehler.me.uk/animation/e_and_m_ac_gen_2.htm

Direct and Alternating Current Alternating current reverses the direction of the current in a regular pattern. In North America, generators produce alternating current at a frequency of 60 Hz. The electric current produced by a generator changes direction twice during each cycle of the coil  current changes direction 120 times each second

Transmitting Electrical Energy Once electricity is produced by generators in the power plants, how is it transmitted to our houses? When electrical energy is transmitted along power lines, some of the electrical energy is converted into heat. Why? Since power lines have resistance, some portion of the electrical energy is lost as heat as the wires get hot. Since the length of the power lines increases the resistance, large amounts of heat can be produced. How can we reduce the amount of heat produced?

Transformers What is Transformer? The high voltages should be reduced before the electricity comes into our houses  safety!! A transformer is a device that increases or decreases the voltage of an alternating current. A transformer is made of a primary coil and a secondary coil. These current carrying wire coils are wrapped around the same iron core.

Transformers As an alternating current passes through the primary coil, the coils magnetic field magnetizes that iron core. The magnetic field in the iron core changes direction at the same frequency with the alternating current. This changing magnetic field in the iron core induces an alternating current in the secondary coil.

Transformers The voltage in the primary coil is the input voltage  Vin The voltage in the secondary coil is the output voltage  Vout The number of turns in the primary coil  Np The number of turns in the secondary coil  Ns Vout / Vin = Ns / Np Using this relationship we can define two types of transformers: Step-Up and Step-Down

Step-Up Transformers Step-Up transformers increase the voltage so that the output voltage is greater than the input voltage.

Step-Down Transformers Step-Down transformers decrease the voltage so that the input voltage is greater than the output voltage.