Rays from sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object?
Answers
Since its discovery, fire has become such an integral part of our everyday lives that most of us take for granted. But what would our species do without it?
It’s been hundreds of thousands of years since prehistoric humans discovered the dancing flames of fire. Since then, it’s become such an integral part of our everyday lives that most of us take for granted.
But what would our species be like without it? Would our lives be the same without cooked food? How would we function once the sun went down? And how would a lack of fire affect our intelligence? Here’s what would happen if we never discovered fire.
If stock markets existed during early human years, you can bet that every cave-dweller would’ve invested all they had into a crazy new discovery called fire. Arguably the most important discovery of all time, Fire is a means of survival. Over the years it’s provided cooked food, warmth, weapons, technology, medical solutions, jobs, and much more.
Without fire, not only would the world around us be completely different but so would we. We wouldn’t look the same, eat the same, or even think the same. But how could a simple source of heat and light affect the entire evolution of our species?
As the story goes, fire was probably discovered when something natural like a lightning storm triggered a wildfire.
But what if that fire burned out before any Neanderthal had noticed it? And as a result, fire was never discovered!
Yes, this is really simplifying things, as it’s believed that fire was discovered many times by many different groups all over the world, but humor me for a second.
If we didn’t discover fire, human beings would be a lot different than we are today. For one thing, we’d be a lot less productive, and we’d spend a lot more time in bed.
Have you ever been so busy that you find yourself wishing for more hours in the day? Well, you should be happy with the amount you have because before fire humans’ activities were mostly limited to daylight hours.
The ability to control light allowed humans to extend their time awake into the later hours of the day. The modern human spends about 16 hours actively awake, that’s double the time of most other mammals who can’t control fire.
If we didn’t have fire, the quality of our sleep would also be affected. How soundly do you think you’d sleep if you had to constantly worry about being attacked by predators overnight? Probably not great, right?
Our deepest level of sleep is called REM, or “Rapid Eye Movement.” This state is where we have our most vivid dreams, and our brain develops long-term procedural memories. Without these kinds of memories, we wouldn’t be able to retain skills, and repeat previously learned tasks.
Using fire to keep predators away allowed early humans to safely fall into REM sleep, improving our ability to master complex tasks – like tool manufacturing.
But perhaps the biggest thing that fire introduced to us was the art of cooking. If those magical flames never came into our lives, we wouldn’t have ovens to give us our favorite pizzas, or grills for our hamburgers, or even pasteurization to make our ice cream.
The heat of the fire not only killed harmful bacteria living in raw meat, it also made the food softer and easier to chew. If it weren’t for cooking, we’d all still be walking around with large jaws and big strong teeth, capable of tearing through the rough fibers of raw meat.
However, our appearance would be the least of our problems, because our brains would also be a lot smaller than they are today. In order for our brains to develop, they need energy in the form of calories. Cooked food not only releases more calories than raw, but it also requires less energy to chew and digest.
The extra calories were put to good use, allowing our hungry brains to become bigger and more powerful. Because we shifted that energy to our heads instead of our guts, we evolved to have larger brains and smaller digestive systems than most other mammals.
You never know what the next big innovation will be to change our evolution the way that fire did. Maybe one day all our food will come in pill form, and we won’t have to spend any energy at all digesting it. But, that’s a story for another day.
Answer:
The ray diagram illustrates that, in case of a concave mirror, the image size becomes equal to the object size when the object distance equals the radius of curvature, i.e, twice the focal length.
So, the object has to be placed at a distance of (15×2)=30 cm in front of the concave mirror.