Frequency and Effects of Radiation
Aligned to HS-PS4-4 — Next Generation Science Standards.
What this lesson teaches
The energy of electromagnetic radiation rises with frequency (E = hf). Low-frequency waves like radio and microwaves mostly heat or vibrate matter, while high-frequency ultraviolet, X-rays, and gamma rays carry enough energy per photon to break chemical bonds and damage DNA, which is why they are called ionizing.
Worked examples
Example 1
A microwave photon and a UV photon may hit your skin, but the UV photon has thousands of times the frequency, so E = hf makes its energy thousands of times greater, enough to break bonds in DNA and cause sunburn, while the microwave only jostles water molecules as heat.
Example 2
This is the line between ionising and non-ionising radiation, and it is set by frequency, not by intensity or by how alarming the name sounds.
Example 3
A radio tower puts out enormous power at a frequency far too low to break a chemical bond; a little UV at the beach does it easily.
Practice questions
- State how photon energy changes as frequency increases.
- Explain why ultraviolet light can cause skin damage but the radio waves passing through you constantly do not.
- Evaluate this claim: 'Any radiation is dangerous if it is bright enough.' Judge it using the difference between energy per photon and total brightness.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Frecuencia y Efectos de la Radiación
La energía de la radiación electromagnética aumenta con la frecuencia (E = hf). Las ondas de baja frecuencia como la radio y las microondas en su mayoría calientan o hacen vibrar la materia, mientras que la ultravioleta, los rayos X y los rayos gamma, de alta frecuencia, llevan suficiente energía por fotón para romper enlaces químicos y dañar el ADN, por lo que se llaman ionizantes.
Ejemplo 1: Un fotón de microondas y un fotón de luz ultravioleta pueden golpear tu piel, pero el fotón ultravioleta tiene miles de veces la frecuencia, así que E = hf hace su energía miles de veces mayor, suficiente para romper enlaces del ADN y causar quemaduras de sol, mientras que el de microondas solo agita las moléculas de agua como calor.
Ejemplo 2: Esta es la línea entre radiación ionizante y no ionizante, y la fija la frecuencia, no la intensidad ni lo alarmante que suene el nombre.
Ejemplo 3: Una torre de radio emite una potencia enorme a una frecuencia demasiado baja para romper un enlace químico; un poco de UV en la playa lo hace fácil.
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