Physics Unit 4

Unit Overview – Electromagnetism

The big picture stuff: Students are introduced to concepts related to electricity, magnetism and electromagnetism in elementary grades. The NGSS has an emphasis on electromagnetism in middle school, however, students haven’t yet had this level of instruction. Electromagnetism is a major focus area for the AP Physics B exam.

Next Generation Science Standards – High School (NGSS-HS):

PS2-5. Plan and conduct an investigation to provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current.

Core ideas: Forces at a distance are explained by fields (gravitational, electric, and magnetic) permeating space that can transfer energy through space. Magnets or electric currents cause magnetic fields; electric charges or changing magnetic fields cause electric fields.

PS3-1. Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.

Emphasize: explaining the meaning of mathematical expressions used in the model. Focus one basic algebraic expressions or computations; to systems of two or three components; and to electric fields.

Core ideas: Energy cannot be created or destroyed, but it can be transported from one place to another and transferred between systems. Mathematical expressions, which quantify how the stored energy in a system depends on its configuration (e.g. relative positions of charged particles). Energy is a quantitative property of a system that depends on the motion and interactions of matter and radiation within that system. That there is a single quantity called energy is due to the fact that a system’s total energy is conserved, even as, within the system, energy is continually transferred from one object to another and between its various possible forms.

PS3-5. Develop and use a model of two objects interacting through electric or magnetic fields to illustrate the forces between objects and the changes in energy of the objects due to the interaction.

Examples: models could include drawings, diagrams, and texts, such as drawings of what happens when two charges of opposite polarity are near each other, including an explanation of how the change in energy of the objects is related to the change in energy of the field. Limit to systems containing two objects.

Core ideas: When two objects interacting through a field change relative position, the energy stored in the field is changed.

Science and Engineering:

• Develop and use a model based on evidence to illustrate the relationships between systems or between components of a system.
• Create a computational model or simulation of a phenomenon, designed device, process, or system.
• Plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence, and in the design: decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of the data (e.g., number of trials, cost, risk, time), and refine the design accordingly.

Cross-cutting concepts:

• Empirical evidence is required to differentiate between cause and correlation and make claims about specific causes and effects.
• Science assumes the universe is a vast single system in which basic laws are consistent.
• Cause and effect relationships can be suggested and predicted for complex natural and human designed systems by examining what is known about smaller scale mechanisms within the system.
• Models can be used to predict the behavior of a system, but these predictions have limited precision and reliability due to the assumptions and approximations inherent in models.

California Science Standards:

5a. Students know how to predict the voltage or current in simple direct current (DC) electric circuits constructed from batteries, wires, resistors, and capacitors.

5b. Students know how to solve problems involving Ohm’s law.

5c. Students know any resistive element in a DC circuit dissipates energy, which heats the resistor. Students can calculate the power (rate of energy dissipation) in any resistive circuit element by using the formula Power = IR(potential difference) I(current) = I2R.

5e. Students know charged particles are sources of electric fields and are subject to the forces of the electric fields from other charges.

5f. Students know magnetic materials and electric currents (moving electric charges) are sources of magnetic fields and are subject to forces arising from the magnetic fields of other sources.

5h. Students know changing magnetic fields produce electric fields, thereby inducing currents in nearby conductors.

5k.* Students know the force on a charged particle in an electric field is qE, where E is the electric field at the position of the particle and q is the charge of the particle.

5l.* Students know how to calculate the electric field resulting from a point charge.

Investigation and Experimentation Standards:

a. Select and use appropriate tools and technology (such as computer-linked probes, spreadsheets, and graphing calculators) to perform tests, collect data, analyze relationships, and display data.

b. Identify and communicate sources of unavoidable experimental error.

c. Identify possible reasons for inconsistent results, such as sources of error or uncontrolled conditions.

d. Formulate explanations by using logic and evidence.

e. Solve scientific problems by using quadratic equations and simple trigonometric, exponential, and logarithmic functions.

g. Recognize the usefulness and limitations of models and theories as scientific representations of reality.

j. Recognize the issues of statistical variability and the need for controlled tests.