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35 Cards in this Set
- Front
- Back
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What are the two units for pressure? |
Pascals or N/m |
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How do you find the centre of mass of an irregular object? |
Hang a plumbline; you then have to hang your object freely form three different point on the object. Then draw a pencil line, in line with the plumbline, from each point. Where they cross is the centre of mass. |
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Why are liquids used in hydraulic systems? |
They are virtually incompressible so the pressure is the same everywhere. |
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For an object in circular motion, a force must act towards the centre called...? |
Centripetal force. |
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Increasing the length of a pendulum does what to the time of the swings? |
It increases the time of the swings. |
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What does increasing the mass of the pendulum do to the time of the swings? |
It has no effect on the time of the swings. |
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How will an object topple over? |
An object will topple over when it's centre of mass is outside of the base causing a resultant moment. |
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How do you make an object more stable? |
Lower is centre of mass and widen it's base. |
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As you increase the speed of an object in circular motion, what happens to the force? |
The force increases. |
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What happens to the force acting on an object in circular motion when you reduce the radius? |
The force increases. |
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How do transformers work? |
The A.C in the primary coil makes the soft iron core electromagnetic. It also moves and changes the direction of the magnetic field. This induces a potential difference in the secondary coil. |
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Increasing the number of turns in the secondary coil does what to the voltage? |
It increases it. |
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Where are objects accelerating towards when they are in circular motion? |
Towards the centre. |
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What is an objects centre of mass? |
Where all the mass is concentrated. |
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How do you find the centre of mass of a regular shaped object? |
Where all the lines of symmetry cross. |
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Why are MRI scans more accurate than x-rays? |
They provide a 3 dimensional image and show you different types of tissues. |
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Why are ultrasounds used to scan developing embryos and not x-rays? |
Ultrasounds do not harm the embryo. |
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What can cause longsightedness? |
The eye being too short or not being able to curve your lens enough. This means the focal point of light is behind the retina. |
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What can cause shortsightedness? |
The eyeball being too long or not being able to get your lens flat enough so the focal point is in front of the retina |
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What safety precautions have to be in place when using x-rays? |
Thick lead aprons and walls. You have to be behind a screen when doing it. |
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What are the downsides of MRI scans? |
There is a high risk of cancer. They are expensive. |
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With a pendulum, the number of oscillations per unit of time is known as what? |
The frequency. |
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What name is given to the furthest position from an eye and object can be focussed clearly? |
Far point |
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What name is given to the closest position from an eye and object can be focussed clearly? |
Near point. |
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What is the value of the far point for most humans? |
Infinity. |
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What is the value of the near point in most adults? |
25 cm |
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Is a lens with a negative power is converging or diverging. |
Diverging. |
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Is a lens with a positive power is converging or diverging. |
Converging. |
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Why are the lenses used nowadays flatter than in the past? |
Materials with a higher refractive index are used. |
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How do you work out an object's refractive index? |
Sin(I) ÷ sin(r) |
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What are is the range of sound frequencies an average human can hear? |
20Hz to 20000Hz |
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What can ultrasound be used to treat? |
Kidney stones. |
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What is the film or CCD in a digital camera equivalent to in the eye? |
The retina. |
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If a conductor is parallel to the magnetic field will it experience a force? |
No. |
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What are the units for frequency? |
Hz |
