How Things Work / TUNE - Fall 2017

1.  Why is it that electrons are the easiest particles to manipulate? 2.  What does atomic number (Hydrogen = 1, Helium = 2, etc.) mean? 3.  If two charged particles are pulled apart to 3 times their original distance of separation, how exactly will the force between them change? 4.  A 5-ohm resistor is connected to a 10-volt battery. What current goes through the resistor? 5.  Draw the symbols for battery, resistance and wire.  Draw a schematic for 2 resistors in series.  Draw a schematic for 2 resistors in parallel. 6.  What is strange about magnetic north on the Earth?

Magnetism! Similar to the case of charge, magnetic poles are divided into North and South poles. A North magnetic pole is one that points toward the Earth's magnetic north pole.  This means that the Earth's magnetic north is ACTUALLY A SOUTH POLE (magnetically speaking). Also: - Like poles repel - Opposite poles attract - Each magnet must have at least one North and one South pole (though they may have more than one of each).  There is NO such thing as a magnetic monopole. - Magnetic fields are real, but the lines are imaginary - Field lines indicate the direction that a compass needle would take in the vicinity of the magnetic field. - There are naturally occurring magnetic minerals - a very common one is called magnetite (Fe3 O4) Magnetic north on the Earth is near Ellesmere Island in Northern Canada, several hundred miles from true (geographic) North (the North Pole).  It is moving toward Russia at several miles per year. For gory detail: http://en.wikipedia.org/wiki/North

OK, so about regular circuits: The images represent SERIES CIRCUITS and PARALLEL CIRCUITS. In a  series  circuit, the current is  constant  and is set by the total resistance of the circuit (the sum of the resistors). If you remove one resistor (or light bulb, as in the first image), the current  stops . If the resistors were identical bulbs, having more bulbs would result in dimmer bulbs, since the battery voltage is distributed among them.  Note that the sum of the voltages "over" the bulbs is equal to the total voltage provided by the battery (give or take some minor losses).  Identical bulbs (or resistors) have identical voltages "over" them - 3 identical bulbs connected to a 9-V battery would have roughly 3-V each over them. In  parallel  circuits, current has multiple paths to take, so the total resistance of the circuit is actually LESS than if the resistors were alone or in series with other resistors - see details below. Since the bulbs are c

Thus far, we have only discussed "static" (stationary) charges.  Static charges alone are useful, but not nearly as much as charges in motion.  As you recall, electrons are the most easily moved particles.  However, for sake of ease in sign convention (positive vs. negative), we define the following: Current  (I) - the rate at which positive charge "flows" I = Q/t The unit is the coulomb per second, defined as an  ampere  (A).  Just as one coulomb is a huge amount of charge (nearly 6.3 billion billion protons), one ampere (or amp) is a tremendous amount of current - more than enough to kill a person.  In fact, you can feel as little as 0.01 A.  Typical currents in a circuit are on the order of mA (milliamperes). Essentially, current is how quickly charge travels (or charge per time, q/t).  The unit (a coulomb per second) is called the ampere (or amp, A).  To keep things simple, we think about positive charge moving, even though it is really all about

Intro to electricity Electricity I - Charge! Charge - as fundamental to electricity & magnetism as mass is to mechanics Charge is a concept used to quantatively related "particles" to other particles, in terms of how they affect each other - do they attract or repel?  If so, with what force? Charge is represented by letter Q. The basic idea - likes charges repel (- and -, or + and +) and opposite charges attract (+ and -). Charge is measured in units called coulombs (C).  A coulomb is a huge amount of charge, but a typical particle has a tiny amount of charge: - the charge of a proton is 1.6 x 10^-19 C.  Similarly, the charge of an electron is the same number, but negative, by definition (-1.6 x 10^-19 C).  The negative sign distinguishes particles from each other, in terms of whether or not they will attract or repel.  The actual sign is arbitrarily chosen. The charge of a neutron is 0 C, or neutral. But what IS charge? Charge is difficult to define.  It is property of p

1.  Show how to compute the wavelength of the radio signal 107.9 MHz.  Note that MHz means 'million Hz." 2.  Concert A is defined as 440 Hz.  Find the following frequencies: a.  the next 2 A's that come after this one (one and two octaves above) b.  A#, which is one note immediately after concert A c.  the wavelength of a concert A note.  Assume that the speed of sound is 340 m/s. 3.  An ambulance siren has a 1000 Hz frequency.  Answer the following questions with:  greater than 1000 Hz, equal to 1000 Hz, less than 1000 Hz.  What frequency do the following people hear? a.  ambulance driver b.  person who the ambulance has passed c.  person who the ambulance is approaching d.  driver who is driving in the opposite direction of the ambulance, after the ambulance has passed 4.  What exactly causes refraction? 5.  Draw the rays that result from the Rays below: .