Physics · 9th Grade · Electricity and Magnetism · Weeks 19-27

Applications of Electromagnetism

Exploring real-world applications of electromagnetic principles in technology and daily life.

• Common Core State Standards
• HS-PS2-5
• HS-ETS1-2

About This Topic

Electromagnetic principles underpin a broad range of technologies that shape daily life in the US, from the MRI scanner in a hospital to the electric motors in a hybrid car to the antennas in every wireless device. Understanding these applications requires synthesizing the individual concepts developed throughout the Electricity and Magnetism unit: fields, forces, induction, and wave propagation.

MRI (magnetic resonance imaging) uses a powerful superconducting magnet to align hydrogen nuclei in the body, then uses radio-frequency EM waves to perturb and detect those nuclei. The spatial variation of magnetic field strength allows a computer to reconstruct a three-dimensional image of soft tissue without ionizing radiation. This contrasts with X-ray imaging, where tissue contrast comes from differential absorption of ionizing radiation.

Active learning is well suited here because applications problems require students to identify which underlying principle applies in each context. Design challenges, case-study analysis, and structured debates about societal impact push students to move from recalling facts to evaluating trade-offs and constructing explanations, the higher-order skills emphasized in the Next Generation Science Standards.

Key Questions

1. How do MRI machines use strong magnetic fields and radio waves to create images of the body?
2. Design a simple device that utilizes electromagnetic principles.
3. Evaluate the societal impact of electromagnetic technologies, from communication to medical imaging.

Learning Objectives

• Analyze how electromagnetic induction is applied in generators and transformers to transmit electricity.
• Evaluate the role of magnetic fields and radio waves in medical imaging technologies like MRI.
• Design a simple device, such as an electromagnet or a basic motor, demonstrating a core electromagnetic principle.
• Compare and contrast the societal benefits and drawbacks of widespread electromagnetic technologies, such as wireless communication and medical devices.

Before You Start

Magnetic Fields and Forces

Why: Students need to understand the nature of magnetic fields and how they exert forces on moving charges and other magnets to grasp applications like motors and MRI.

Electric Current and Circuits

Why: Knowledge of electric current is fundamental, as many applications of electromagnetism involve the relationship between electricity and magnetism, such as in electromagnets and induction.

Electromagnetic Waves

Why: Understanding that light and radio waves are forms of electromagnetic radiation is crucial for comprehending applications like MRI and wireless communication.

Key Vocabulary

Electromagnetic Induction	The production of an electromotive force (voltage) across an electrical conductor in a changing magnetic field. This is the principle behind electric generators.
Superconducting Magnet	A powerful magnet made from materials that have zero electrical resistance when cooled to very low temperatures, essential for creating the strong magnetic fields in MRI machines.
Radio Frequency (RF) Waves	A type of electromagnetic wave used in technologies like MRI and wireless communication. In MRI, they are used to excite atomic nuclei.
Electromagnet	A type of magnet in which the magnetic field is produced by an electric current. Electromagnets can be turned on or off, and their strength can be adjusted.

Watch Out for These Misconceptions

Common Misconception

MRI and X-ray both use the same kind of radiation to image the body.

What to Teach Instead

X-ray imaging uses ionizing electromagnetic radiation that passes through tissue; denser tissue blocks more X-rays, creating contrast. MRI uses a strong magnetic field and non-ionizing radio-frequency waves to detect hydrogen nuclei. The two technologies use completely different EM principles and excel at imaging different tissue types.

Common Misconception

Wireless technologies (Wi-Fi, Bluetooth, cell phones) work by sending data through physical cables embedded in the air.

What to Teach Instead

Wireless technologies transmit information by modulating electromagnetic waves, varying their frequency or amplitude to encode data. The waves travel through empty space and matter at the speed of light without any physical medium. This is direct evidence that EM waves require no material carrier.

Common Misconception

Electromagnetic technologies are purely beneficial with no significant risks or trade-offs.

What to Teach Instead

Every EM technology involves trade-offs: MRI requires managing powerful magnetic fields that can attract metal implants; high-voltage transmission lines create electric and magnetic fields in surrounding areas; radio spectrum is a finite resource requiring careful management. Evaluating these trade-offs is part of engineering and science literacy.

Active Learning Ideas

Case Study Analysis: MRI vs. X-Ray

Provide groups with a one-page brief comparing the physics of MRI and X-ray imaging. Groups complete a two-column organizer identifying the EM principle involved, the wave or field type used, whether radiation is ionizing, and the tissues best imaged. Groups share findings and the class builds a comparative summary of when each technology is the better clinical choice.

35 min·Small Groups

Design Challenge: Simple EM Device

Challenge pairs to sketch a simple device using electromagnetic principles (examples: a magnetic door latch, a reed switch, a coil speaker, a simple solenoid actuator). They label the operating principle, identify the input and output energy forms, and estimate whether the device requires AC or DC. Pairs present their sketches in a rapid two-minute gallery walk.

40 min·Pairs

Socratic Seminar: EM Technology and Society

Students review two short articles on electromagnetic technologies (one on wireless communication infrastructure, one on medical imaging access disparities) before class. The facilitator poses: 'Which EM technology has had the greatest positive societal impact, and what responsibilities come with it?' Students build a structured argument using evidence from physics and the readings.

30 min·Whole Class

Gallery Walk: EM Applications Map

Post seven stations around the room, each showing an application (MRI, wireless charging, electric motor, radio antenna, microwave oven, transformer, generator) with a brief description. Student groups annotate each station: which core EM principle applies, what the energy input and output are, and one way the application could fail if the underlying physics were not carefully engineered.

30 min·Small Groups

Real-World Connections

• Engineers at General Electric design and test advanced MRI scanners used in hospitals like the Mayo Clinic to diagnose a wide range of medical conditions, from neurological disorders to sports injuries.
• Technicians at power substations across the United States maintain large transformers that use electromagnetic induction to efficiently step up or step down voltage for long-distance electricity transmission.
• Researchers at Tesla utilize principles of electromagnetism to develop and improve the electric motors and battery management systems in their vehicles, impacting the automotive industry.

Assessment Ideas

Exit Ticket

Provide students with a scenario: 'A new type of wireless charging pad is being developed.' Ask them to identify one specific electromagnetic principle that must be applied and briefly explain how it works in this context.

Discussion Prompt

Pose the question: 'Considering both the benefits and potential risks, how should society regulate the development and use of powerful electromagnetic technologies like 5G networks or advanced medical imaging?' Facilitate a class discussion where students present arguments for and against stricter regulations.

Quick Check

Show students images of three devices: an electric motor, an MRI machine, and a radio antenna. Ask them to label each device and write one sentence for each explaining the primary electromagnetic principle it utilizes.

Frequently Asked Questions

How does an MRI machine create images of the inside of the body?

An MRI machine uses a very strong magnetic field (typically 1.5-3 Tesla) to align hydrogen nuclei (protons) in the body's water molecules. A radio-frequency pulse then knocks the protons out of alignment. As they realign, they emit a detectable radio signal. By varying the magnetic field strength across the body, the scanner maps where each signal originated, reconstructing a detailed 3D image of soft tissue.

What electromagnetic principles are used in everyday wireless communication?

Cell phones, Wi-Fi, and Bluetooth all transmit information by modulating radio-frequency EM waves. Data is encoded by varying the wave's frequency, amplitude, or phase. The waves travel through air and building materials (they are non-ionizing and low-energy), are received by an antenna, and decoded back into data. The underlying physics is the same as for AM/FM radio, just at higher frequencies.

What societal problems have electromagnetic technologies helped solve?

EM technologies address major societal challenges: MRI enables non-invasive diagnosis of brain and soft-tissue disease; electric motors power zero-emission vehicles; wireless communication connects people across geographic and economic barriers; the power grid, built on generators and transformers, makes industrial society possible. Each application reflects decades of engineering refinement of the same core physics.

How does active learning benefit students studying electromagnetic applications?

Applications topics require students to transfer principles from the unit into new contexts, a skill that lecture does not build well. Case studies, design challenges, and structured debates push students to identify which principle applies, evaluate trade-offs, and construct arguments, the exact higher-order thinking that NGSS engineering practices require and that prepares students for science and engineering careers.