# Physics P3

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How are x-rays used in hospitals?
To make images and CT scans OR to destroy tumors
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What is a disadvantage to x-rays?
Can damage human tissue and cause cancer.
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What are x-rays absorbed by?
Bones and teeth
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What aren't x-rays absorbed by?
Tissue/skin
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What do CT scans distinguish?
Differences between tissue and bone (or teeth).
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What frequency are ultrasound above?
20,000HZ
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Where are ultrasound waves used in?
Used in medicine for ultrasonic scanning OR destruction of kidney stones.
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Why is a ultra sound more safe than a x-ray?
It's non-ionising.
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What is reflective index?
Measure of how much a substance can refract a light ray.
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What is the algebraic term for refractive index?
n
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What's for the formula for n= ?
sin I / sin R
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What is the critical angle?
Angle of incidence of a light ray in a transparent substance that produces a refraction above the boundry.
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What happens if the critical angle is hit/matched?
Total internal reflection occurs.
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What is an endoscope used for?
Used to see inside of the body directly.
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When does total internal reflection occur?
When the incidence ray angle in a transparent substance (such as water) is greater than the critical angle.
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What does a converging (convex) lens do?
Focuses parallel rays to a point, called the principal focus.
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What does a diverging (concave) lens do?
Makes parallel rays spread out as if they come from the principal focus point.
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What type of image is formed by a converging (convex) lens?
'Real image' if the object is further away than the principal focus, then too by a convex lense.
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What type of image is formed by a diverging (concave) lens?
'Virtual image' and if the object nearer to the lense than the principal focus, it's also produced by a converging lens.
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What's the equation for magnification?
image height/object height
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What type of lens does a camera contain and what type of image is produced?
Converging lens that's used to form a real image of an object.
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What type of lens is a magnifying lens and what type of image is formed?
Converging lens which forms a virtual image.
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What is light focused by in the eye?
Onto the retina by the cornea and eye lens.
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What's the range of human eye?
25cm to infinity and beyond.
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How does refractive index influence how thick/thin a lens can be?
The higher the refractive index, the flatter and thinner it can be.
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What is the moment of a force?
A measure of the turning effect of the force on an object.
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What is the centre of mass of an object?
Where an object's mass may thought to be concentrated and balanced.
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What happens when a suspended object is in equilibrium?
Centre of mass is directly below the point of suspension.
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How can we find the centre of mass of an object?
A plumb line
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How can you make a object more stable?
Make it heavier, or have a wider base (such as on a tractor).
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For an object in equilibrium, the sum of anti clock moments = ?
= the sum of clockwise moments around that point.
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What would cause a object to topple?
If the line of action/centre of mass is outside the base.
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The pressure of a hydraulic fluid is?
Acts equally in all directions so equal/the same.
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What does a hydraulic system use?
Pressure in a fluid to exert a force.
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Pressure = ? / ?
force / area
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What is the unit of pressure?
Pascal (PA) which is equal to 1N/m(2)
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Why is the velocity of a object moving in a circle constantly changing?
The object is constantly changing direction so as is it's velocity.
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What is centripetal acceleration?
The acceleration towards the centre of the circle of an object moving around the circle.
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What does the centripetal force of an object depend on? Give 3 answers.
It's mass, speed and radius of the circle.
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What does the time period of a simple pendulum depend on?
It's length.
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How can you workout the time period of the pendulum?
Measure the average time for 20 oscillations and / by 20.
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## Other cards in this set

### Card 2

#### Front

What is a disadvantage to x-rays?

#### Back

Can damage human tissue and cause cancer.

### Card 3

#### Front

What are x-rays absorbed by?

### Card 4

#### Front

What aren't x-rays absorbed by?

### Card 5

#### Front

What do CT scans distinguish?