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Concept of density. This YouTube video will provide information about the concept of density. It’s great to use as an introduction to the topic or as a way to summarise the topic.

There are many different processes and phenomena that emit electromagnetic radiation. Humans have taken advantage of many of these processes to develop technologies that use electromagnetic radiation.

The beauty of a coral reef, the warm radiance of sunshine, the sting of sunburn, the X-ray revealing a broken bone, even microwave popcorn—all are brought to us by electromagnetic waves. The list of the various types of electromagnetic waves, ranging from radio transmission waves to nuclear gamma-ray (γ-ray) emissions, is interesting in itself.

Even more intriguing is that all of these different phenomena are manifestations of the same thing—electromagnetic waves (see Figure 15.1). What are electromagnetic waves? How are they created, and how do they travel? How can we understand their widely varying properties? What is the relationship between electric and magnetic effects? These and other questions will be explored.

Photoelectric materials emit electrons when they absorb light of a high-enough frequency.

This 32 minute long YouTube video investigates the water contamination problems in Tanzania, with specific focus on Dar Es Salaam. 

This 11 minute long YouTube video describes the various causes and types of water pollutants.

This YouTube video investigates what water pollution is and some examples and effects of water pollution.