Transcript Chapter 14
Magnetism and EOCT Additions Boyle’s Law A law stating that the pressure of a given mass of an ideal gas is inversely proportional to its volume at a constant temperature. 2. A gas law stating that the pressure and volume of a gas have an inverse relationship when temperature is held constant. 3. If pressure increases, then volume ____________________and vice versa, when temperature is constant. According to this law, the pressure exerted by a gas held at a constant temperature varies inversely with the volume of the gas. For example, if the volume is halved, the pressure is doubled; and if the volume is doubled, the pressure is halved. The reason for this effect is that a gas is made up of loosely spaced molecules moving at random. If a gas is compressed in a container, these molecules are pushed together; thus, the gas occupies less volume. The molecules, having less space in which to move, hit the walls of the container more frequently and thus exert an increased pressure. http://en.wikipedia.org/wiki/Boyle%27s_law Practice Problem A balloon was inflated to a volume of 5.0 liters at a pressure of 0.90 atm. It rises to an altitude where its volume becomes 25.0 liters. Will the pressure around the balloon increase or decrease? What was the new pressure? Practice Problem A fountain pen which has a total volume of 2.4 cm3 is half full with ink at the surface where the pressure is 780.0 mmHg. It is put in a pilot's pocket who flies to an altitude where the pressure is 520.0 mmHg. How much ink leaks out of the pen? Plasma! Plasma has neither a definite volume nor a definite shape. Plasma often is seen in ionized gases. Plasma is distinct from a gas because it possesses unique properties. Free electrical charges (not bound to atoms or ions) cause plasma to be electrically conductive. Plasma may be formed by heating and ionizing a gas. Example Stars are made of plasma. Lightning is plasma. You can find plasma inside fluorescent lights and neon signs. *Charles’ Law 1. Charles's law (also known as the law of volumes) is an experimental gas law which describes how _____________tend to ______________when heated. 2. At constant pressure, the volume of a given mass of an ideal gas increases or decreases by the same factor as __________________on the absolute temperature scale (i.e. the gas expands as the temperature increases) 3. The physical law that the volume of a fixed mass of gas held at a constant pressure varies ____________________with the absolute temperature 4. What kind of relationship? Application/Examples A container holds 50.0 mL of nitrogen at 25° C and a pressure of 736 mm Hg. What will be its volume if the temperature increases by 35° C? A sample of helium has a volume of 521 dm3 at a pressure of 75 cm Hg and a temperature of 18° C. When the temperature is increased to 23° C, what is the volume of the helium? Imagine a balloon filled with helium on a cold winter day. While you are in the shop, the balloon is normal. As you step outside the balloon begins to shrivel up. This happens because of the temp. of the helium in the balloon deceases and becomes less dense, because the helium particles lose energy and become more concentrated, decreasing the volume. But when you put the balloon in a warm area, it goes back to its original size Bell Ringer Which of the laws that we have discussed applies to the diagram on the next slide? Magnetism! Some materials can be made into permanent magnets Examples: Lodestones (magnetic all the time) Any piece of iron can be changed into a permanent magnet through conduction Magnets exert a ______________ force on each other Magnetic Pole An area of a magnet where the magnetic force appears to be the______________. Magnetic Field: a region where a magnetic force can be detected Application: Compasses used to analyze magnetic fields and determine direction Earth’s Magnetic Field Works like a bar magnet Has north and south poles Source of magnetic field is still being debated Magnetic poles not the same as geographic poles. Section 2: Magnetism from current! Electric currents can produce magnetic fields The magnetic field of a coil of wire resembles that of a bar magnetic Solenoid! Solenoid A long, wound coil of insulated wire When attached to current a magnetic field is created More loops or more current = stronger magnetic field Electromagnet A strong magnet created when an_____________ core is inserted in to the center of a current carrying solenoid The solenoid magnetizes the iron rod. The iron rod increases the magnetic field of the solenoid. Electromagnetic Devices Galvanometer: an instrument that measures the amount of current in a circuit. Electric Motor: A device that converts electrical energy into ________________ energy. A motor uses magnets to create motion. Stereo Speakers: use magnetic force to produce____________ Electric motor Electric Currents from Magnetism Electromagnetic Induction: the production of current in a conducting circuit by a ______________in the strength, position, or orientation of external magnetic field. * an electric current can be produced in a circuit by changing a magnetic field* Electromagnetic Induction As a loop of wire moves in and out of a magnetic field, a current is_____________. Generators A device that uses electromagnetic induction to convert mechanical energy to ______________energy. Opposite of …. Alternating Current: an electric current that changes direction at regular intervals. Application: Generators used at home are AC, current supplied to home outlets DC= Direct current. One Direction for the pathway. Transformers A device that can change one alternating current voltage to a different alternating current voltage. Transformers can increase or decrease voltage