S4 Fri Comb Sci 5:30pm Yuan Ching Prelim Paper 2 by Mochi Maltese

S4 Fri Comb Sci 5:30pm Yuan Ching Prelim Paper 2 by Mochi Maltese https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4 Post your working here en-us 2021-05-28 09:39:18 UTC 2024-10-15 01:27:00 UTC hello@padlet.com https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659271789 1A] As sound is produced , the molecules around the speaker vibrates which then cause air molecules that are further away to vibrate as well causing them to vibrate and eventually producing a sound wave. 👌 This also creates region of compression and rarefaction

]]> 2021-07-23 09:39:53 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659271789 1a. https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659271828 when sound is played, the speaker drum vibrates. the air particles next to it vibrates, collides and transfers energy to the neighbouring air particles 👌 which sets up and alternating series of compression and rarefactions in the air. 👌 it travels through the air as longitudinal waves to all parts of the room]]> 2021-07-23 09:39:57 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659271828 q1 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659272370 b) Frequency of 20 khz is the audible frequency range for a human where pitch can be heard.

Note: Answer is not checking about the audible hearing range of human but what does frequency of 20 kHz is interpreted as 20000 waves are produced in 1 second.

c) v = f x wavelength
340 = 20000 x wavelength
wavelength = 0.017 m ❌ 17m (longest wavelength)]]> 2021-07-23 09:40:56 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659272370 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659272842 The ~~particles~~ cone of the loudspeaker will vibrate and push and pull the neighbouring air molecules then travels as a longitudinal waves. The vibration causes a displacement in the particles around it causing regions of rarefactions and compressions to be produced 👌]]> 2021-07-23 09:42:00 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659272842 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659275833 1) Sound is produced when the speaker vibrates, this causes the neighbouring air molecules to vibrate as well.👌 The vibration passes from one layer of air to the next and Regions of compression and rarefaction is produced. 👌]]> 2021-07-23 09:47:36 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659275833 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659278184 It means the highest pitch a human can hear is 20000 hertz. ❌

Answer: 20000 waves are produced in 1 second.]]> 2021-07-23 09:52:19 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659278184 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659278746 1bi] It means that the number of waves (20,000) produced in a second which can be heard by a human is as large as 20 kHz. 👌

1bii] v= f x ^
^ = 340 / 20 000
=0.017m ❌ 17m (longest wavelength)

2b] a=v-u / t
= 45-20/60
= 0.417 . m/s^2 👌

2c] F=ma
= 1200 x 5/12
= 500 N 👌

3a] W= mass x g
mass= 2.6 / 10
=0.26 kg 👌

3b] d= m/v
mass = 0.80 x 250
= 200g
= 0.20kg 👌

4b] 0.20 x 50 = 0.60 x w
10N = 0.60 x w
w = 10 x 0.60
=6 N ❌

4c]

5a] gravitational potential energy
= mgh
= 1.6 x 10 x 1.0
=16 J
KE = 1/2 mv^2
16 = 1/2 x1.6 x v^2
V^2=20
V= 4.47m/s 👌

b]

6a] Sterilisation of Dental equipment
~~wireless networks,~~ (UV is too ionising to be used for wireless networks. Only radio waves and low frequency microwaves are used)

6b] common property: they are transverse waves 👍

different: they have different frequencies 👍

]]> 2021-07-23 09:53:28 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659278746 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659279664 20kHz is 20000 waves produced per second 👌]]> 2021-07-23 09:55:25 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659279664 1bi https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659280615 it means that the highest pitch that humans are able to hear is 20kHz❌

Answer: 20000 waves are produced in 1 second.]]> 2021-07-23 09:57:19 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659280615 Q2 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659281668 b) 45 - 20 / 60
= 0.41666
= O.417 m/s^2 (3.SF) 👌

C) F = ma
F = 1200 (0.416666)
= 500N 👌]]> 2021-07-23 09:59:30 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659281668 1bii https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659281845 v=fλ
λ=v/f
λ=340/f
λ=340/ 20
λ=17m 👌

]]> 2021-07-23 09:59:49 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659281845 1bii https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659282200 speed = frequency x wavelength
wavelength = speed/ frequency
wavelength = 340/20
=17m 👌]]> 2021-07-23 10:00:39 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659282200 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659284041 2b)(45-20)/60
=0.41666
=0.417 m/s^2(3sf) 👌
2c) FR=ma
resultant force = 1200kg x 0.416666 = 500N 👌

]]> 2021-07-23 10:05:34 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659284041 3a) https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659286831 W=mg
weight = m x 10
2.6= m x 10
m= 0.26kg 👌

b) mass of methanol= density x volume
mass= 0.8 x 250
= 200g
=0.2kg 👌

]]> 2021-07-23 10:12:36 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659286831 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659290503 2021-07-23 10:21:20 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659290503 Q3 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659292069 A) W = mg
2.6 = m(10)
m = 0.26 kg 👌

b) density = m /v
0.8 = m / 250
m = 312.5 g
= 0.3125 kg ❌ (0.2 kg)

Note: mass = density x volume

]]> 2021-07-23 10:25:34 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659292069 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659295016 25 m/s ❌
( 0.417 m/s)]]> 2021-07-23 10:33:48 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659295016 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659296459 500.4 N Round off to 500N
( 500 N)]]> 2021-07-23 10:37:34 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659296459 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659296554 2b)25/60= 0.417m/s^2 👌
2c) f=ma
=1200 x 0.41667 = 500 N 👌]]> 2021-07-23 10:37:50 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659296554 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659297268 4b)total moments= force x perpendicular distance
anticlockwise= clockwise
0.40 x 70 + 0.2 x 50
=38Nm 👌
4c) sum of CW = sum of anti clockwise
38Nm = 0.8 x force at b
b = 38/ 0.8
= 47.5N👌

]]> 2021-07-23 10:39:36 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659297268 Q5 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659298050 a) PE = mgh
= (1.6)(10)(1.0)
= 16J
KE=1/2MV^2
16=1/2 (1.6) V^2
V^ = 20
V = 4.4721
= 4.47m/s (3.sf) 👌

b) ]]> 2021-07-23 10:41:42 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659298050 0.26kg 👌 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659298315 2021-07-23 10:42:25 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659298315 3a https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659298846 2.6/10=0.26kg 👌]]> 2021-07-23 10:43:50 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659298846 0.2kg 👌 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659298995 2021-07-23 10:44:15 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659298995 3b https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659299733 mass= density x volume
=0.80x250=200g
=0.2kg 👌]]> 2021-07-23 10:46:21 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659299733 Q4 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659301475 b) 0.20 x 50 =0.60 x W
10 N = 0.60W
W = 6 N ❌]]> 2021-07-23 10:51:02 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659301475 Q6 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659303211 a) ultraviolet : sunbeds/ sterilization of medical equipment
microwaves : microwave oven cooking of food /satellite television (Note: microwave oven is a device and not a purpose of microwave. The purpose is to cook food)

b) common property : They are transverse waves 👍

different property: microwave have a lower frequency than ultraviolet.
👍

]]> 2021-07-23 10:55:47 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659303211 Q7 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659304665 a) The black heat sink is made of metal which is a good ~~absorber~~ conductor of heat, which allows heat to go to the heat sink rather than the computer chip. 👍

2nd feature: ???
The heat sink in black in colour which is a good emitter of heat which helps the heat sink to radiate heat faster.

b) as the heat sink gains heat, it gains kinetic energy and thermal energy. Molecules in the heat sink start to vibrate about fixed position more vigorously and the average spacing between them increases 👍]]> 2021-07-23 11:00:00 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659304665 4b. https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659305031 total moments

= 70x0.8+50x0.2

=66

]]> 2021-07-23 11:01:00 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659305031 Q9 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659307718 Pd = RI
= 3(1.5)
=4.5 V 👍

b) 12 - 4.5 = 7.5 v
R=V/I
6.0=7.5 /I
I = 0.8 A ❌

]]> 2021-07-23 11:07:51 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659307718 Q10 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659314573 a) P = F/A
=300/20 👍
=20N/CM^2 (typo error)

B) 15 N/cm²(pressure inside the piston is same throughout)

(c) Valve A will open and oil flows from reservoir into Piston P, Valve B will close, Piston Q remains unchanged. ]]> 2021-07-23 11:13:52 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659314573 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659316423 5a) by using principal of conservation of energy, gpe = ke
gpe=mgh
= 1.6 x 10 x 1
=16
KE = 1/2 mv^2
16= 1/2 x 1.6 x v^2
v^2 =20
v= 4.47m/s 👌
b)

]]> 2021-07-23 11:18:23 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659316423 Q11 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659317273 (b) Inverted and enlarged ✔✔
(c) projector 👍

(d) The image will be dimmer. Reason: Less light from the object would pass through the lens to form the image.

(ei) critical angle = sin90/sin40
= 1.5557
=1.56 (3.sf) ❌ They want the critical angle, not the refractive index
1.54=sin90/sini
critical angle= 40.492=40.5 (1dp) 👍👍

]]> 2021-07-23 11:20:38 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659317273 Q12 kristendanielratnam https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659317316 (a) p=v^2 / R
100=240^2/R
R = 576 ohms 👍👍

(b) 100W = 0.1kwh
cost=0.1 x 5 x 0.24
=$0.12 ✔✔]]> 2021-07-23 11:20:46 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659317316 5a. https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659317370 GPE= mgh=1.6x 10x 1=16
KE = 1/2 mv^2=16
v^2= 8/1.6
=5
v=2.24m/s (3sf) ❌

]]> 2021-07-23 11:20:53 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1659317370 6 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664881299 ai) used in tanning beds to help people achieve suntan
aii)microwave oven to cook food
b) common property: they are both transverse waves 👍
different property: they have different frequency 👍]]> 2021-07-30 09:31:33 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664881299 7 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664882881 a) one feature would be the metal fins. since metal is a good conducter of heater it would conduct the heat of the computer chip preventing it from over heating
another feature would be that the metal fins are black as black is a good emitter of heat through radiation

The metal fins have a large combined surface area , that allows heat to be radiated more quickly (radiation depends on exposed area) and heat lost faster through convection current due to more greater surface area of contact.]]> 2021-07-30 09:35:36 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664882881 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664885386 7a] The heat sink is painted black and black surfaces are better absorbers and emitter (note: heat sink needs to help chip dissipate heat) of infrared radiation which cause thermal energy to be transferred easily away from the chip.

The heat sink is also made out of metal. ~~Metal has a shiny surface which caused heat to be reflected easily.~~ Metals are good thermal conductors and heat produced by the chip is conducted away quickly.

7b] As the heat sink gains heat, they vibrate about their fixed positions more vigorously and their molecules would be arranged slightly further apart. 👍👍

8.

9a] V=IR
= 1.5 x 3.-
=4.5 V 👍

b] potential difference at z
=12- 4.5 = 7.5 V
I of z = 7.5 / 6.0
=1.25 A. 👍]]> 2021-07-30 09:40:24 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664885386 i) https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664889338 both are trans verse waves/ 👍
ii) diff wavelengths and frequencies 👍]]> 2021-07-30 09:49:27 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664889338 7 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664893607 Black metal fins help with thermal energy ~~transferrence~~ transfer as it is made of metal hence it is a good conductor of heat, this means heat energy is conducted away quickly from the chip and prevents any over heating.

~~good conductors mean good~~ The black matt paint of the fins allows the heat sink to be good absorber and emitter of radiation and so heat energy can be radiated away from the chip quickly. ]]> 2021-07-30 09:59:25 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664893607 7b https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664896863 as idk

As the temperature rises, the molecules in the heat sink vibrate more vigorously.
The average spacing between the molecules increases.]]> 2021-07-30 10:07:20 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664896863 9 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664897606 a) V=IR=1.5x3=4.5 V 👍
b) I=V/R= 4.5/6=0.75 ❌ 1.25A]]> 2021-07-30 10:09:32 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664897606 7b https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664898696 Molecules in the sink gain heat and kinetic energy, they start vibrating in their spots. Hence the spaces between the molecules increase. 👍]]> 2021-07-30 10:12:30 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664898696 Q6 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664905439 ai) sunbeds (UV is used to help people get tanned in a sunbed)

Note: Sunbed is a device that produces the ray so cannot be considered usage of the UV rays.

aii)Microwaves are used to cook food
b) common property: they are both transverse waves. 👍
different property: they have different frequencies. 👍

7a) First feature :This is because the heat sink is ~~made out of a metal~~.painted black colour ~~Metals~~ Black surfaces are good absorbers and emitters of radiation compared to bright/shiny sufaces which helps the metal sink to radiate heat faster than non metals and allows it to cool faster.

Second feature: The heat sink is made of metal, which is a good conductor of heat. This allows heat to be conducted away from the chip faster by the heat sink to prevent any overheating.

b) Once the heat sink absorbed radiation, it gains heat which causes a gain in kinetic energy. The molecules]]> 2021-07-30 10:29:52 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664905439 10 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664913295 ai) P=F/A= 300/20=15N/cm^2 👍
aii)15N/cm^2 👍
aiii)F=AxP=400x15=6000
bi)volume=basexheight=20x5=100cm^3
bii) height= volume/base=100/400=0.25cm 👍👍
c)nothing will happen to valve a, (OPEN) valve b will close 👍 and piston q will move down ❌
Nothing will happen to Piston Q

d) this is because the particles in air are much further apart which will be compressed when pressure is applied unlike oil which particles are closely packed allowing it to move but making it hard to be compressed]]> 2021-07-30 10:52:10 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664913295 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664914013 10 a] P= F / A = 300 / 20 = 15N cm^2 👍

10(b) 15 N/cm²(pressure inside the piston is same throughout)

]]> 2021-07-30 10:54:12 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664914013 10 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664914039 ai) pressure= force/area
pressure= 300N/20cm^2
= 15N/cm^2 👍
ii) 15N/cm^2 👍
iii)force= area x pressure
force= 400 x 15
= 6000 N 👍
bi) volume= 20 x 5
= 100cm^2 3
bii) volume= base area x height
height=volume/ base area
= 100/400 = 0.25cm
C) nothing will happen to all of them. This is because when x is lifted up, they will all go back to their original positions and values and hence there will be no change.❌ Valve A will open and oil flows from reservoir into Piston P, Valve B will close, Piston Q remains unchanged.

d) This is because air does not have a fixed volume and hence when the hydraullic pressed is pushed down, the air from the surrounding atmosphere might make it harder to press down due to air particles being hard to compress.
]]> 2021-07-30 10:54:17 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664914039 10a https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664917552 15n/cm2]]> 2021-07-30 11:04:08 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664917552 10b https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664917621 15n + (pressure of piston q)????
= 15 N/cm²(pressure inside the piston is same throughout) ]]> 2021-07-30 11:04:21 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664917621 6000N 👍 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664919489 2021-07-30 11:10:11 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664919489 20x5= 100 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664920973 2021-07-30 11:14:02 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664920973 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664923974 10aiii] Pressure= F/A
Force= Pressure x area
=400 x 15
= 6000N 👍

b] volume= base area x height
= 20 x 5
= 100cm^3 👍
bii]
volume = base area x height
height= base area / volume
= 100 / 400
=0.25 cm 👍]]> 2021-07-30 11:21:36 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664923974 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664925279 (400xd= 100
d= 100/400
= 0.25cm 👍]]> 2021-07-30 11:24:25 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1664925279 11 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670926663 b) ~~upright~~ and enlarged 👌 (Note: cannot be upright since the image is reverse that of the object)-- enlarged and real *👍

c) magnifying glass?? ❌
Note: Magnifying glass produces virtual image. Hence the correct answer should be "projector"

d) there would be no change ❌ as the light rays only passes through the bottom half to reflect. (Note: The size and focus of the image remains the same. However, due to lesser light rays forming the image, it becomes dimmer)

e) sin c= 1/n
c=sin^-1(1/1.54)
=40.5 degrees ( 3 sf ) ✔✔]]> 2021-08-06 09:47:37 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670926663 11b https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670926895 11b

Image is larger (please use "magnified or enlarged"), inverted and real and ~~further~~

Note: Further is not an image property.

]]> 2021-08-06 09:48:10 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670926895 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670927470 11 b enlarged and inverted ✔✔

11c microscope ❌ projector

11d the image produced would be smaller ❌ Image would be dimmer. Reason: Less light from the object would pass through the lens]]> 2021-08-06 09:49:34 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670927470 qn 11 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670927504 real and inverted ✔✔
c) magnifying glass ❌
Note: Magnifying glass produces virtual image. Hence the correct answer should be "projector"

d) the image will now become ~~blured~~. This is because when the top half is blocked, ~~one~~ some of the rays are unable to reach to the point👍 . Hence, the image will look ~~blur~~
Note: blurred object happens because the light rays did not focus well. If less amount of light forming image, the image will be "dimmed" .

ei) n=1/sin c
= 1/1.54
=40.5(3sf) ✔✔
ii)

Note

]]> 2021-08-06 09:49:39 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670927504 11c https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670929753 spectacles ❌ projector

]]> 2021-08-06 09:53:44 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670929753 11d https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670931563 image produced will be ~~darker~~ dimmer
Reason: Less light from the object would pass through the partially blocked lens.]]> 2021-08-06 09:58:15 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670931563 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670932174 11ei] sin c=1/n
c=sin^-1 [1/1.54]
=40.49
=40.5 degress ✔]]> 2021-08-06 09:59:28 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670932174 qn12 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670932929 i) P=IV
100= I(240)
I=100/240
=5/12
R=V/I
R= 240/5/12
=576ohm ✔✔

aii) (Note: 100 W = 0.1 kW so the amount of energy usage should be 5x0.1 = 0.5 kWh so the cost = 0.24 x 0.5 = $0.12)

12b) This is so that the wires do not recieve any excess current from the wire to prevent overheating.❌ (overheating is NOT possible if there is no short circuit)

When the wires are switch, the resistance of the wires are also different which may result in a surge of current flowing through the wires which might melt the protective layer of the wire and might cause a short circuit if the exposed wire comes into contact with the other wires. ❌

This is because wire A has a switch connected to it.
So when the switch is open, the appliance will be disconnected from the high voltage live wire. Thus preventing the possibility of electric shock to the user.

c) wire B. ❌ Wire C (this is the earth wire). Under normal operation, no current should flow through earth wire.

]]> 2021-08-06 10:01:24 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670932929 12 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670933706 ai) R=V/I
= 240/100=2.4 ❌ idk how to find the symbol but yes

(Note: The 100W is power. So you can use the formula P=V^2/R --> R = V^2/P = 240²/100 = 576 ohm

aii)(Note: 100 W = 0.1 kW so the amount of energy usage should be 5x0.1 = 0.5 kWh so the cost = 0.24 x 0.5 = $0.12)

b) this is because when the switch is off, it will cause the circuit to open and there would be no more current flowing towards the bulb anymore. unlike when the ( I realised I read the question wrong ) nvrm ✔✔

Update: This is because wire A has a switch connected to it. So when the switch is open, the appliance will be disconnected from the high voltage live wire. Thus preventing the possibility of electric shock to the user.

c) wire b ❌ Wire C (this wire is the earth wire) there should not be any current flowing under normal operating conditions.

]]> 2021-08-06 10:03:27 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670933706 11e https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670934220 1.54= 1/sin(c)
c= sin-1(1/1.54)
= 40.5 ✔✔]]> 2021-08-06 10:04:32 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670934220 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670934374 12 a i] P=v^2 / R
R= v^2/ P
=57600V / 100 W
= 5760 ohm ✔✔ ( careless calculation mistake)

12aii] cost of lamp 1 day
=0.24 x 5 x ~~100~~
=$120 ❌ $0.12

(Note: 100 W = 0.1 kW so the amount of energy usage should be 5x0.1 = 0.5 kWh so the cost = 0.24 x 0.5 = $0.12)

]]> 2021-08-06 10:05:03 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670934374 q12 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670949029 a) i] 100= 240(240)/R
R= 240(240)/100
= 576 ohm ✔✔

ii] $1.20 ❌(Note: 100 W = 0.1 kW so the amount of energy usage should be 5x0.1 = 0.5 kWh) Hence the cost will work out to be $0.12

b) That way there wont be overheating of cables as if it was connected to the live terminal, it would carry the current from the terminal to the bulb but with the wire a being connected, it will carry through wire A and then to wire b to light up the bulb.❌

Note: Overheating is due to electrical fault e.g. frayed live wires touching neutral wire or casing.

This is because wire A has a switch connected to it.
So when the switch is open, the appliance will be disconnected from the high voltage live wire. Thus preventing the possibility of electric shock to the user.

c) Neutral Wire. ❌ Wire C (earth wire) since under normal operation, the casing should NOT be live.

]]> 2021-08-06 10:44:07 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670949029 https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670966722 12 b there are many plugs connected to wire a if wire A is connected to the live terminal it would reduce the current This is because wire A has a switch connected to it.
So when the switch is open, the appliance will be disconnected from the high voltage live wire. Thus preventing the possibility of electric shock to the user.

12c wire c ✔
12 d not sure]]> 2021-08-06 11:24:49 UTC https://padlet.com/gregorywong_sg/3b2y7qqntqcuo7b4/wish/1670966722