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Flashcards in Part 3 Deck (38)
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1

what happens in transverse waves?

transverse waves oscillate at right-angles in the direction of the wave

2

what happens in longitudinal waves?

in longitudinal waves like sound, energy oscillates in the same direction as the wave travels

3

what is the equation for frequency (Hz)?

1/time

4

why does refraction occur?

refraction occurs when light enters a medium of different density at an angle, causing it to change speed and direction. When leaving the material the ray is bent back into its original direction. (The denser the material, the higher the refractive index)

5

what are the uses of electromagnets?

1. circuit breakers- used to break the circuit if the electrical current is too high
2. relays- using one circuit to turn another circuit on and off
3. loudspeakers- convert electrical energy into sound energy

6

how can you increase the strength of an electromagnet?

- increase the current
- increase the number of coils
- add an iron core

7

how do we find the direction of a magnetic field around a wire?

using the right hand grip rule

8

what do you need to make an electromagnet?

- a current
- coil of wire

9

what is meant by 'magnetically hard'?

substances that can be permanently magnetised. Often alloys of iron, nickel and cobalt

10

what is refraction?

when light enters a medium of different density causing it to change speed (slow down) and direction

11

what is a method to calculate refractive index?

1. draw around your shape (a perspex block)
2. draw along your beams of light; going in and coming out of the shape (the light at an angle to the block)
3. connect the two lines through the middle
4. draw a normal and measure the angle of incidence and refraction to that normal
5. use n=sin i/ sin r to calculate refractive index

12

what is meant by a uniform magnetic field?

when magnetic field lines are the same distance apart from each other, we say that the magnetic field is uniform

13

what are the two different speed equations?

1. wavespeed (m/s) = frequency (Hz) x wavelength (m)

2. wavespeed= distance/time

14

describe images in a mirror?

- laterally inverted
- virtual image is the same distance away as real
- virtual image is the same size as real

15

what is ultrasound?

ultrasound is sound more than 20,000 Hz. It is used by bats and dolphins to 'see' as it echoes helping them to gauge distances. It is also used for baby scans because of safety; there are no dangers to the baby

16

what is the correlation between the angle of incidence and the angle of reflection?

angle of incidence= angle of reflection

17

what is the equation for the critical angle

Sin C= 1/n

18

what is total internal reflection?

when light is incident at greater than the critical angle, it reflects. This can be used to trap light fibres

19

what is the efficiency equation?

useful energy output/ total energy input

20

what are the uses and dangers of the EM waves?

- radiowaves- radio and TV
- microwaves- heat up food and used in phones- can cause internal heating of body tissues
- infra-red- heat detecting and TV remote- can cause skin burns
- visible light- to see/ vision- damages eyes
- ultra-violet- crime scenes, detect fingerprint/blood etc. check for fake money- can cause sun burn= skin cancer
- x-rays- to see bone- can cause cancer if exposed too much
- gamma rays- sterilise equipment, can kill cancer cells (radiotherapy)- cell mutations can lead to cancer

21

what is dispersion?

the splitting of white light by a prism

22

what is the order of dispersion?

Red- longest wavelength, lowest frequency
Orange
Yellow
Green
Blue
Indigo
Violet- shortest wavelength, highest frequency

23

what will happen when a magnet is put next to a compass?

a magnet next to a compass will cause it to change direction. It will override earth's magnetic field.

The earth's north pole is a magnetic south pole

24

what is meant by magnetically soft?

substances that can only be temporarily magnetised. Alloys with less iron, nickel and cobalt will be magnetically soft and have a weaker magnetic field

25

define wave

waves are a transfer of energy which travel outwards from a source

26

what are the advantage of electromagnets?

- you can turn it on and off
- you can control the strength

27

what do the thumb and fingers represent in the right hand grip rule?

Thumb= direction of current

Fingers= direction of magnetic field

28

which magnetic metals are magnets made from?

iron, nickel and cobalt. These are ferrous metals

29

what is the wave equation?

wavespeed (m/s)= frequency(Hz) x wavelength (m)

30

what is meant by frequency?

number of waves passed in a second (Hertz)