https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm Post your questions and attempts here en-us 2021-05-28 11:41:47 UTC 2025-12-29 18:11:45 UTC hello@padlet.com https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659327123 from 0s to 10s, there is a constant acceleration.👌 From 10s to 20s, there is a decreasing acceleration. 👌]]> 2021-07-23 11:44:17 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659327123 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659327769 the acceleration is zero constant (cannot be zero acceleration since there is a NET FORCE = 580N )❓ from 0 to 10s and it starts to decrease at a constant rate from 10 to 20s.👌  ]]> 2021-07-23 11:45:53 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659327769 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659328298 1(a) from t=0s to t=10s, acceleration is constant.👌 from t=10s to t=20s, acceleration is decreasing uniformly. 👌]]> 2021-07-23 11:47:12 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659328298 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659329732 the acceleration of the bicycle is constant from 0s to 10s but starts to decrease constantly from 10s to 20s  👌]]> 2021-07-23 11:50:42 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659329732 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659330726 bi) 3.87m/s^2 square  👌
bii) 40.7m/s  👌]]> 2021-07-23 11:52:55 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659330726 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659332155 (b)(i) F=ma
          600-20=150a
          a=3.87m/s^2 👌]]> 2021-07-23 11:56:13 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659332155 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659333139 (b)(ii) a=(v-u)/t
           3.87=(v-2.0)/10
           38.7=v-2.0
           v=40.7m/s  👌]]> 2021-07-23 11:58:43 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659333139 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659333243 bi) 3.87 m/s^2  👌
bii) 40.7 m/s  👌]]> 2021-07-23 11:59:00 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659333243 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659333662 bi. 3.87m/s^2  👌
bii. 40.7m/s  👌]]> 2021-07-23 12:00:04 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659333662 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659336104 (b)F=ma
600N=150a
a=4  ❌ Pls note that the net force = 580 N]]> 2021-07-23 12:04:20 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659336104 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659338968 b(ii)600-20=150a
a=v-u/t
v=40.7 ms^-1 ]]> 2021-07-23 12:10:51 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659338968 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659344941 The block can be tilted more before it topples as the centre of gravity will be lower when the height of the block is lowered.  👌]]> 2021-07-23 12:23:32 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659344941 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659345465 when the height of the block is reduced, the block can be tilted more to the right without toppling over because its centre of gravity is lower   👌]]> 2021-07-23 12:24:39 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659345465 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659346434 (c) Reduced height of the block enables the block to be tilted more before it topples as centre of gravity of the block is lowered.  👌]]> 2021-07-23 12:26:30 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659346434 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659346678 when the height is reduced, the block can tilt more towards the right without toppling over  as the centre of gravity is lowered making the block more stable   👌]]> 2021-07-23 12:27:02 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659346678 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659347059 P=hpg
   =(0.3)(13600)(10)
   = 40800 Pa
Pressure of air = 40800 + (1.0)(10^5) 
                           = 140800 Pa ❌


correction : 121760 Pa  👌]]> 2021-07-23 12:27:57 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659347059 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659352091 3(a) P(air)= P(atm) + P(mercury)
                  = 1.0*10^5 + hpg 
                  = 1.0*10^5 + (0.38-0.22)(13600)(10)
                  =121760Pa  👌]]> 2021-07-23 12:36:34 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659352091 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659352137 121760 Pa  👌

]]> 2021-07-23 12:36:39 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659352137 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659352145 P = hpg
h = 380-220
   = 160mm
   = 0.16m
P = (0.16)(13600)(10)
   = 21760 Pa
Pressure of the air in the flask 
= 21760+ (1.0 x 10^5) 
= 121760 Pa  👌

]]> 2021-07-23 12:36:39 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659352145 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659359545 3b) when the air in the flask starts to cool, it’s temperature decreases and hence the molecules move slower (have less KE) and hit the walls of the flask less frequently and with lesser force . this causes the air pressure to decrease and therefore, the mercury level decreases.  👌]]> 2021-07-23 12:50:22 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659359545 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659361123 3(b) lower temperature of air in the flask decreases the kinetic energy of gas molecules. frequency of collisions between the molecules and the walls of the container decreases and with less force, pressure of gas molecules decreases, resulting in a decrease in mercury levels  👌]]> 2021-07-23 12:52:59 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659361123 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659363387 Work is the product of the force and distance moved by the object towards the direction of the force ]]> 2021-07-23 12:56:42 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659363387 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659364087 4(a) work done is the product of the force and distance moved by the object in the direction of the force.]]> 2021-07-23 12:57:54 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659364087 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659364425 4a) Work is the force multiplied by the distance travelled in the direction of the force.]]> 2021-07-23 12:58:33 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659364425 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659364942 work is the product of the force and the distance moved by the object in the direction of the force ]]> 2021-07-23 12:59:37 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659364942 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659365578 Q3Work done is energy taken for a specific force  to move an object over a distance.]]> 2021-07-23 13:00:51 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659365578 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659367126 4(b)
GPE at B = KE at C
mgh = 1/2 mv^2
10(12) =1/2 v^2
v^2 = 240
v = 15.5 m/s (3d.p.)]]> 2021-07-23 13:03:43 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659367126 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659367422 15.5m/s (3sf)]]> 2021-07-23 13:04:13 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659367422 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659379728 100 J]]> 2021-07-23 13:21:29 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1659379728 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1670995225 the cold junction is placed in an unknown liquid with unknown temperature, thus, the temperature of the surrounding air cannot be determined as the temperature of one junction have to be known to determine the temperature of the other junction. 👍👍]]> 2021-08-06 12:22:24 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1670995225 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1670996017 24 deg C ✔]]> 2021-08-06 12:23:45 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1670996017 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1670997922 5i) the cold junction is placed in a liquid of unknown temperature and hence, knowing the potential difference will not help in identifying the temperature of the surrounding air because it can only be determined when the temperature of the liquid is known. 👍👍]]> 2021-08-06 12:26:47 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1670997922 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1670998439 5(a)(i)
The final temperature of the liquid is not known hence the decrease in thermocouple reading cannot be used to identify the temperature of the surrounding air, 👍👍

]]> 2021-08-06 12:27:37 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1670998439 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671027964 5ii) 24 deg c ✔]]> 2021-08-06 13:12:24 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671027964 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671029000 24 degree celsius  👌👌]]> 2021-08-06 13:13:42 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671029000 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671032186 5(ii) 
24 degrees celsius ✔]]> 2021-08-06 13:17:30 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671032186 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671032586 5b) when the walls of the capillary are not uniform, this causes the area of the capillary to be bigger and hence, when the liquid in the thermometer rises up, the reading on the thermometer will be lower than it is supposed to be, giving an inaccurate temperature reading. 👍👍👍]]> 2021-08-06 13:18:00 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671032586 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671034510 5(b)
There is a difference in diameter of the capillary hence, there is greater pressure ❓❓ on the lower part of the thermometer, hence increasing ❌ (decreasing) the height of volume of liquid in the thermometer, giving an inaccurate reading. 👌👌]]> 2021-08-06 13:20:21 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671034510 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671453640 6a) frequency = 4.17 x 10^14 Hz ✔✔
(Note: Don't forget the unit)]]> 2021-08-07 01:37:54 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671453640 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671454789 6bi) infra-red rays ✔]]> 2021-08-07 01:41:31 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671454789 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671454922 6bii) remote control of electrical appliances  ✔]]> 2021-08-07 01:41:53 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671454922 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671457751 7ai) angle of incidence = 41.7 deg (1dp) ❌ 22.1 degrees]]> 2021-08-07 01:50:45 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671457751 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671459153 7aii) R2 does not exit the bottle after the first refraction because it undergoes total internal reflection where its angle of incidence is greater than the critical angle. 👍👍 (also mention that light is travelling from denser medium into less dense medium)]]> 2021-08-07 01:54:31 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671459153 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671466870 7b) Total internal reflection will occur in the bottle. Hence, the light rays entering the bottle will be able to exit through the base of the base of the bottle and light up large parts of the house interior. Without the bottle, sunlight can only reach parts of the house. ]]> 2021-08-07 02:14:45 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671466870 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671469147 7c) radiation. the sun's energy travels to earth as electromagnetic waves which is known as infra-red radiation. when absorbed, the energy of the infra-red radiation transforms into thermal energy of the receiving body. (can pass through vacuum)]]> 2021-08-07 02:20:56 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671469147 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671470140 2021-08-07 02:23:39 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671470140 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671472094 8bi) steel ❌ Soft iron (speakers need to constantly magnetise and demagnetise to vibrate the cone of the speakers to produce sound) ]]> 2021-08-07 02:28:27 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671472094 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671472356 8bii) steel is a hard magnetic material and hence it is difficult to lose its magnetism once magnetised, making it a permanent magnet. thus, it is suitable.]]> 2021-08-07 02:29:08 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671472356 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671475144 9a)
Minimum distance = 500 x 10^-6 x 330
                                = 0.165m ❌ Distance = 1/2 x 0.165m = 0.0825 m (since 0.165m is the distance travelled by sound and its echo)]]> 2021-08-07 02:35:59 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671475144 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671481286 9b)
Minimum distance = 3 x 10^8 (This is speed of light not sound) x 500 x 10^-6 = 150000m  ❌ 75000 m



The equipment which transmits and receives radio waves would be more useful because it can detect the time delay from a greater distance. huh? The radio wave version detects shorter distance but more appropriate compared to detecting wall from 75 km away?!]]> 2021-08-07 02:46:23 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671481286 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671493282 10a) V=IR
Current through Lamp 3 = 7.60 - 1.90 = 5.70A
Resistance of Lamp 3 = 200/ 5.70 = 35.1 ohms (3sf) 👌👌]]> 2021-08-07 03:16:48 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671493282 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671497321 10b) 
R1 = 200/0.4 = 500 ohms
R2 = 200/1.5 = 133 ohms
R3 = 35.1 ohms
effective resistance = 26.3 ohms 
power = (7.60^2) (26.3) = 1519.088W
energy used = 1519.088 x 110/60 x 7 = 19494.96267 Wh
= 195 kWh
cost = 19.5 x 0.22 = $4.29 (nearest cent) 👍👍]]> 2021-08-07 03:28:23 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671497321 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671567924 11ai)
200MJ = m x 4.2 x 10^3 x (25-14) --> change in temp is (45-25)
200 x 10^6 = m x 4.2 x 10^3 x 11
m = (200 x 10^6) / (4.2 x 10^3 x 11)
m = 4329.004
m = 4330 kg (3sf)  ❌ 2380 kg]]> 2021-08-07 06:52:38 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671567924 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671570971 12a) ohm's law states that the current through a metallic conductor is directly proportional to the potential difference across the ends of the conductor, provided the temperature and other physical conditions remain constant. 

]]> 2021-08-07 07:03:26 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671570971 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671571469 12b) the filament lamp does not obey ohm's law because its resistance increases as the current increases]]> 2021-08-07 07:05:18 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671571469 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671573430 12c) the resistance of the lamp increases when the potential difference is increased. V=IR when V and I are both increasing, R will also increase.]]> 2021-08-07 07:11:48 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671573430 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671573914 12di) variable resistor]]> 2021-08-07 07:13:38 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671573914 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671574624 12dii) a variable resistor has a fixed resistance and hence, current has to pass through it first before passing through the lamp. this will decrease the current through the lamp.]]> 2021-08-07 07:16:00 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671574624 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671574923 12ei) electrical current = 0.05A (from the graph)]]> 2021-08-07 07:17:03 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671574923 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671575494 12eii) 
V = IR
2.5V = I x 200 ohms
I = 2.5/200
I = 0.0125A]]> 2021-08-07 07:18:55 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671575494 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671578510 13 (either)
a) current is flowing from A to D. using Fleming's left-hand rule, the magnetic field represented by the index finger is pointing to the left. the middle finger which represents the current is pointing into the paper and hence current flows from A to D.]]> 2021-08-07 07:28:18 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671578510 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671579673 2021-08-07 07:32:13 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671579673 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671580532 13c) commutator. the commutator rotates together with the coil. it allows the coil to rotate by reversing the current in the coil in every half-turn]]> 2021-08-07 07:35:17 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671580532 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671581024 13d) using stronger magnets, increasing the number of turns of the coil, increasing the current flow and winding the coil around a soft-iron cylinder]]> 2021-08-07 07:37:08 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671581024 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671582794 11b) the average daily sunshine duration for Fiji is only 4 hours a day. solar energy is used for heating up the interior of the house. with only 4 hours of sunshine a day, the solar energy absorbed is insufficient for maintaining the indoor temperature at 25 deg c for Fiji 👍👍 Fiji will need (7.17 x 0.84) = 6 hrs of sunshine]]> 2021-08-07 07:42:35 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671582794 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671585258 11c) steel. steel is dark-coloured (what?! Steel is silver in colour, you can use black paint to get it dark) and hence, it is a good absorber of infra-red radiation. this will allow a lot of sunlight to be absorbed to maintain the indoor temperature of the house. Just state that it is a good conductor of heat. ]]> 2021-08-07 07:48:39 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671585258 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671589557 13 (or) 
ai) positive]]> 2021-08-07 08:02:03 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671589557 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671589871 2021-08-07 08:03:04 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671589871 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671590426 13aiii) the tension in the string]]> 2021-08-07 08:05:10 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671590426 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671591290 13bi) the negative charges of the sphere will flow to the ground, leaving the positive charges]]> 2021-08-07 08:06:29 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671591290 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671591736 13bii) the sphere will move further away from the plate because they are both positively charged and hence, they repel]]> 2021-08-07 08:07:52 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671591736 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671592238 2021-08-07 08:09:38 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1671592238 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678059873 6(a) frequency = 4.17 x 10^14 Hz ✔
6(b)(i) Infra-red rays ✔
6(b)(ii) Used in lasers ❓❓ (laser is a different technology)
Infra-red is used in remote control, heating elements, intruder alarms)]]> 2021-08-13 11:41:35 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678059873 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678059980 Infrared ray ✔

]]> 2021-08-13 11:41:44 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678059980 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678060257 a) 4.17 x 10^14 Hz ✔
bi) infrared ✔
bii) infrared cooker ✔]]> 2021-08-13 11:42:07 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678060257 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678060652 treating skin injuries 👌 (Note: This application is quite rare e.g. applicable to burn victims so better to name more common applications like remote control, burglar alarm or heating element)]]> 2021-08-13 11:42:46 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678060652 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678061883 22.1 deg ✔

]]> 2021-08-13 11:44:36 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678061883 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678064232 Total internal reflection occurs, as the ray is travelling from a denser medium to a less dense medium, and the angle of incident is larger than the critical angle. ✔ (excellent answer)]]> 2021-08-13 11:48:36 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678064232 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678064282 ai) 22.1 degree celsius 👍👍
aiii) The angle experiences total internal reflection as the angle of incidence is greater than the critical angle   👍👍   (also mention that light is travelling from denser medium into less dense medium)]]> 2021-08-13 11:48:41 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678064282 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678071921 7(a)(i) Incidence angle = 22.1 degree celcius ✔
7(a)(ii) Angle of incidence greater than critical angle, hence total internal reflection occurs and R2 does not exit the bottle (also mention that light is travelling from denser medium into less dense medium) 👍👍
7(b) not sure
7(c) Radiation. Thermal energy is transferred in the form of electromagnetic waves and the infra-red radiation produces a warm feeling on the boy since only radiation can pass through vacuum to reach Earth from the sun. ]]> 2021-08-13 12:01:09 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678071921 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678074882 As total internal reflection will occur in the bottle, the bottle can trap light, thus, lighting up the room better than just the plastic sheet. (Not really "trap" light but allows more light to exit via the bottom half of the bottle) ]]> 2021-08-13 12:06:26 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678074882 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678075628 Radiation. Heat is transferred as a form of infrared radiation from the sun to the boy. (can pass through vacuum)]]> 2021-08-13 12:07:46 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678075628 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678076200 Steel ❌ Soft iron (speakers need to constantly magnetise and demagnetise to vibrate the cone of the speakers to produce sound) ]]> 2021-08-13 12:08:41 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678076200 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678082143 Steel is a hard magnetic material, which is suitable for making permanent magnet as it is hard for steel to lose its magnetism.❌ ]]> 2021-08-13 12:17:40 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678082143 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678082313 8(a)(i) magnetic field lines on the left and right and drawn curving into the opposite end of the north pole of the magnet 👍👍
8(a)(ii) X is located in between the two magnets. 👍👍

8(b)(i) Steel ❌ Soft iron (speakers need to constantly magnetise and demagnetise to vibrate the cone of the speakers to produce sound)

8(b)(ii) Steel has ferromagnetic properties, hence it is difficult to lose its magnetism after being magnetized, making it a permanent magnet,

]]> 2021-08-13 12:17:58 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678082313 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678086012 0.165 m ❌ Distance = 1/2 x 0.165m = 0.0825 m (since 0.165m is the distance travelled by sound and its echo)]]> 2021-08-13 12:23:20 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678086012 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678089539 bi) steel  ❌ Soft iron (speakers need to constantly magnetise and demagnetise to vibrate the cone of the speakers to produce sound)

bii) Steel is a hard magnetic material which is suitable for making a permanent magnet as steel does not lose its magnetism easily  ]]> 2021-08-13 12:27:50 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678089539 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678089673 The new equipment is more useful as it can detect the time delay at a further diatance compared to the other equipment.
minimum dist. of new equipment ❌ The minimum distance of 75000m is too far and impractical for carpark lot distances.

= (3.0)(10^8) (500)(10^-6) / 2
=75000m 👍👍]]> 2021-08-13 12:28:00 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678089673 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678091840 35.1 ohms (3sf) 👌👌]]> 2021-08-13 12:30:34 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678091840 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678092935 9(a) Minimum distance = 330 x 500 x 10^-6
                                        = 0.165m ❌ Distance = 1/2 x 0.165m = 0.0825 m (since 0.165m is the distance travelled by sound and its echo)

9(b) Minimum distance
= 3 x 10^8 x 500 x 10^-6
= 150000m ❌ 75 000m

The equipment transmitting radio waves is more useful as there is a greater minimum distance to detect the time delay. huh? The radio wave version detects shorter distance but more appropriate compared to detecting wall from 75 km away?!]]> 2021-08-13 12:31:55 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678092935 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678100434 a) 0.165m ❌ Distance = 1/2 x 0.165m = 0.0825 m (since 0.165m is the distance travelled by sound and its echo)

Reason: ??

]]> 2021-08-13 12:40:14 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678100434 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678106554 a)35.1 ohms  👌👌
b) $4.29  ✔

]]> 2021-08-13 12:46:38 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678106554 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678110808 10(a) Resistance of lamp 3 = 35.1 ohms (3s.f.) 👌👌

10(b) Cost = $4.29 (2.d.p.) ✔

]]> 2021-08-13 12:51:01 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678110808 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678119230 $4.29 (nearest cent) 👍👍

]]> 2021-08-13 13:00:07 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678119230 https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678132866 total solar energy = 110x10^6 J (3sf)❌ 310 MJ]]> 2021-08-13 13:14:44 UTC https://padlet.com/gregorywong_sg/hv8o23gpfxkfrhrm/wish/1678132866