Physics II

Electric field lines show how a charged object affects the space around it. A source charge creates an electric field, and that field can exert electric force on another charged object called the test charge. The electric field is a vector at each point in space, so it has both size and direction.

The electric field is the electric force per unit test charge placed at a point. If a charge is placed in that field, the force on it equals the charge times the electric field. This makes electric...

Voltage, or electric potential, describes electric potential energy per unit charge. It is a scalar quantity, and it helps explain many electrical effects. In practice, the difference in electric potential is what matters most.

Changes in electric potential across space are linked to the electric field. That field can produce an electric force on a charge. In a resistor, the difference in electric potential between two points drives electric current flow.

This experiment uses a volt meter and...

Magnetic fields come from moving electric charges and from magnetic materials such as bar magnets. A current is one example of moving charge. The magnetic field made by a current can be calculated with the Maxwell equation.

Bar magnets also create magnetic fields. In magnetic materials, the field comes from tiny charge movements inside the material. These fields can be shown with small compass needle magnets, which turn to line up with the magnetic field.

Magnetic fields push on other moving...

Measuring the electron’s charge-to-mass ratio is the focus of this physics experiment. It recreates J. J. Thomson’s famous experiment from the end of the 19th century. Thomson used it to measure the charge-to-mass ratio of the electron.

This work also connects to Robert A. Millikan’s oil-drop experiment a few years later. Millikan’s result gave a value for the charge of the electron. Together, these experiments let scientists determine the electron’s mass and charge for the first time. Those...

This experiment measures voltage, current, and resistance in basic electric circuits. It also builds skill with circuit diagrams and the terms resistor, resistance, current, voltage, and power supply.

Students learn how to wire a circuit and how to measure current through a circuit component. They also measure the potential difference, or voltage, across a component. These steps help connect circuit symbols with real parts in the lab.

A power supply or battery provides voltage, measured in...

Series and parallel resistor connections change how current and voltage behave in a circuit. This experiment shows how to find the total, or effective, resistance for each setup. It also uses Ohm’s law to relate voltage and current when the resistance is known.

In a series circuit, resistors are wired one after the other. The same current flows through each resistor. Their voltages add together to make the total voltage, so the effective resistance is the sum of the individual resistances.

Capacitors store opposite charges on two conductors, such as two metal plates. This charge separation creates a potential difference, or voltage drop, between the conductors. In this experiment, commercial capacitors and a parallel plate capacitor are used to show how capacitance links charge and voltage.

Capacitance is the proportionality factor between the amount of charge on each conductor and the voltage drop across it. When the voltage changes with time, the current flowing into the...

Magnetic induction in coils is demonstrated with inductive coils and a voltmeter. A rod magnet is inserted into or pulled away from the core of a coil to create a brief electromotive force, or emf, in the coil. The voltmeter measures the resulting voltage change.

The experiment also shows mutual inductance between two coils. When current in one coil is turned on or off, it can induce an emf in a nearby second coil. This makes the link between changing current and a voltage response clear.

RC, RL, and LC circuits show how current and voltage can change over time. These circuits combine resistors, capacitors, and inductors, which each behave differently in an electric circuit. A resistor dissipates energy and follows Ohm’s law, so its voltage is proportional to its current.

A capacitor stores electrical energy. In a capacitor, current depends on how fast the voltage changes. An inductor stores magnetic energy. In an inductor, voltage depends on how fast the current changes.

When...

Semiconductors conduct electricity in ways that depend on temperature and impurity level. Crystalline silicon is the most common semiconductor material. Pure semiconductors are usually not strong conductors, so they are often combined with a small amount of impurity to improve conductivity.

This process is called doping. Donor impurities, such as phosphorus and arsenic, add electrons to silicon. Acceptor impurities, such as boron and aluminum, remove electrons from silicon. When acceptors take...

Photoelectric effect is the emission of electrons from a metal when light shines on it. The key idea is that the light must have a high enough frequency for its photons to carry enough energy. That energy increases with light frequency.

This experiment shows the photoelectric effect with a charged zinc metal plate. The zinc is connected to an electroscope, which is an instrument that shows the presence and relative amount of charge. The plate is then exposed to either a regular lamp or...

Light changes speed when it moves through different materials. When it crosses from one material to another, it may slow down or speed up. That change in speed makes the light bend. This bending is called refraction.

Some of the light is also reflected at the boundary between the two materials. In special cases, the light can bend so sharply that it is completely reflected back into the material it came from. The lab explores the basic law of refraction and shows how this behavior affects...

Laser light can reveal wave behavior through interference and diffraction. These are common wave effects seen in many settings, from water waves to electromagnetic waves such as light.

Interference happens when two waves of the same kind overlap. Their combined wave creates a repeating pattern of larger and smaller amplitude. Diffraction happens when a wave passes through an opening or moves around an object. In that case, different parts of the wave can interfere and produce a similar pattern...

Standing waves on a slinky show how wave superposition and reflection can create stable patterns. These waves, also called stationary waves, appear to stay in place even though the material is moving up and down. They are formed when two waves travel in opposite directions with the same frequency and amplitude.

Standing waves are easy to spot in finite media. A plucked guitar string is a common example. Water in a lake and air in a room can also show this behavior. On a string fixed at both...

Sound waves and motion are the focus of this high school physics experiment. The lesson connects how sound travels through air with how the sound changes when the source moves. It also shows how to measure the speed of sound in air.

Waves are disturbances that move through a material medium or through empty space. Light waves can travel through a vacuum and through some forms of matter. They are transverse waves, which means the oscillations are perpendicular to the direction of travel. Sound...