GCSE Physics Revision "Electric Fields (Triple)"

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Hi, and welcome back to

freesciencelessons.co.uk. By the end of

this video, you should be able to

describe how two charged objects exert a

force on each other. You should then be

able to describe what's meant by an

electric field. And remember that all of

this is for triple physics students

only.

In the last video, we saw that when two

insulators are rubbed together,

electrons can pass from one to the

other. When an insulator gains

electrons, it becomes negatively

charged, and when it loses electrons, it

becomes positively charged. Scientists

call this static electricity. In this

video, we're going to look at this in

more detail. So, let's get

started. I'm showing you here two

plastic spheres. The sphere on the left

has a positive charge and the sphere on

the right has a negative charge. Now the

first key fact that you need to

understand is that objects carrying

opposite charges attract. So that means

that there's a force of attraction

between these two spheres. Scientists

call this a non-cont force because the

two spheres are not

touching. Here we've also got two

plastic spheres, but this time they're

both positively charged. And this brings

us to our second point. Objects carrying

the same type of charge

repel. So in this case, there's a force

of repulsion between these two spheres.

And again, this is a non-cont force.

Now, we saw this in the previous video.

This man's hair is standing on end when

he touches a vandagramraph generator.

That's because each hair is now

positively charged. And that means that

the hairs repel each other and move

apart. Okay. Now scientists explain the

forces of attraction and repulsion

between charged objects using the idea

of an electric field. So let's look at

that.

Now I'm showing you here a charged

object and it's completely isolated from

any other

object. Now this charged object has an

electric field around it. What that

means is that if we place another

charged object near it like this, it

will experience a force. In this case,

because both of the objects have the

same type of charge, this will be a

force of

repulsion. Scientists show an electric

field using field lines like

this. These lines must be perpendicular

to the surface of the object. In other

words, at a 90° angle. So, for example,

this is not correct. The lines are not

perpendicular to the surface.

Now the arrows on the field lines show

the direction of force when a positive

object is brought nearby. So as you can

see in the case of this example, a

positive object experiences a force of

repulsion when it's brought near this

positive charge. The field lines for a

negative object look like

this. Now you can see that if we bring a

positive object near this charge, it

will experience a force of attraction.

We can see that as the arrows are now

pointing inwards towards the charge.

Now if we decrease the distance between

the objects then the force gets

stronger. So this positive object

experiences a strong force of repulsion

and that's because it's close to the

central positive charge. However, this

object experiences a weaker force of

repulsion as it's further away.

Remember, you'll find plenty of

questions on the forces between charged

objects and on electric fields in my

vision workbook, and you can get that by

clicking on the link above. Okay, so

hopefully now you should be able to

describe how two charged objects exert a

force on each other. You should then be

able to describe what's meant by an

electric field.

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