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幾題physics questions plz~
發問:
1) Induced current flowing along one side of the coil of an a.c. generator changes direction alternately, but it is not so for a d.c. generator .點解呢個statement 係錯既 ?2) The density of nitogen is 1.25 kgm^-3 at standard temperature and pressure (ie 0 C and 100kpa ). Determine the density of nitrogen at 42 C and... 顯示更多 1) Induced current flowing along one side of the coil of an a.c. generator changes direction alternately, but it is not so for a d.c. generator . 點解呢個statement 係錯既 ? 2) The density of nitogen is 1.25 kgm^-3 at standard temperature and pressure (ie 0 C and 100kpa ). Determine the density of nitrogen at 42 C and 800kPa . A 0.144 kgm^-3 B 3.42kgm^-3 C 8.67 kgm^-3 D 11.6 kgm^-3 ANS C 唔識做...另外 呢度係咪因為壓力大左 所以個DENSITY 一定會升 ? 3) A coil ABCD is put in a magnetic field . X X X X X XD__CX X X X |__| X X X X A BX X Which of the following can induce a current flowing in the coil ? 1) Move the coil towards the left 2) Increse the magnetic field strength continuously 3) Rotate the coil about DA ANS : 2 & 3 點解1) cannot induce a current ? 唔係有cut of b field 就有 induce current 架咩? 3) 唔明點樣rotate about DA.. 唔該晒~ 更新: 第一題 係咪即係 無論係 dc 同 ac 既 generator 都會有 Induced current flowing along one side of the coil of changes direction alternately ?
1. The structure of a simple dc dynamo and an ac dynamo is basically the same. The difference lies on the connection to the external circuit. A pair pf commutators is used in the dc dynamos, but a pair of slip rings is used in an ac dynamo. Thus, the induced current in one side of the rotating coil always changes its direction in half a cycle, it is the use of the commutators that rectify the induced current to dc. 2. Use ideal gas equation, PV = nRT assume one mole of gas ( n = 1) At STP, 10^5(Vo) = R(273)where Vo is the volume at STP But volume = mass/density hence, 10^5(m/po) = R(273) where m is the mass of gas and po is the density at STP At 800 kPa and 42'C (= 315 K), 8x10^5(V) = R(315) where V is the new volume i.e. 8x10^5(m/p) = R(315) where p is the new density Dividing the two equations: (p/po)(1/8) = 274/315 p = 8 x 273/315 x 1.25 kg/m^3 = 8.67 kg/m^2 3. Statement (1) is wrongAlthough there is cutting of field lines by both the sides AD and BC, you could, by using Fleming's right hand rule, find out that any induced current tends to flow from D to A and also from C to B. Thus these two currents cancel away and no net current is flowing. Be aware that the existence of induced emf in the coil doesn't not necessarily indicate that there is induced current. In this case, the induced emf on AD and BC are opposite in direction and would counter-balance one another, causing no current to flow. Statement (3): The coil rotates with AD as the axis of rotation. This is similar to, but not exactly the same as, what happens in a dynamo with a coil rotating in a magnetic field. There is change of magnetic flux linkage with the coil (or the side BC cuts through field lines). Hence, induced emf and current are produced.
其他解答:0D7DAC4E7B8CAAC5
幾題physics questions plz~
發問:
1) Induced current flowing along one side of the coil of an a.c. generator changes direction alternately, but it is not so for a d.c. generator .點解呢個statement 係錯既 ?2) The density of nitogen is 1.25 kgm^-3 at standard temperature and pressure (ie 0 C and 100kpa ). Determine the density of nitrogen at 42 C and... 顯示更多 1) Induced current flowing along one side of the coil of an a.c. generator changes direction alternately, but it is not so for a d.c. generator . 點解呢個statement 係錯既 ? 2) The density of nitogen is 1.25 kgm^-3 at standard temperature and pressure (ie 0 C and 100kpa ). Determine the density of nitrogen at 42 C and 800kPa . A 0.144 kgm^-3 B 3.42kgm^-3 C 8.67 kgm^-3 D 11.6 kgm^-3 ANS C 唔識做...另外 呢度係咪因為壓力大左 所以個DENSITY 一定會升 ? 3) A coil ABCD is put in a magnetic field . X X X X X XD__CX X X X |__| X X X X A BX X Which of the following can induce a current flowing in the coil ? 1) Move the coil towards the left 2) Increse the magnetic field strength continuously 3) Rotate the coil about DA ANS : 2 & 3 點解1) cannot induce a current ? 唔係有cut of b field 就有 induce current 架咩? 3) 唔明點樣rotate about DA.. 唔該晒~ 更新: 第一題 係咪即係 無論係 dc 同 ac 既 generator 都會有 Induced current flowing along one side of the coil of changes direction alternately ?
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最佳解答:1. The structure of a simple dc dynamo and an ac dynamo is basically the same. The difference lies on the connection to the external circuit. A pair pf commutators is used in the dc dynamos, but a pair of slip rings is used in an ac dynamo. Thus, the induced current in one side of the rotating coil always changes its direction in half a cycle, it is the use of the commutators that rectify the induced current to dc. 2. Use ideal gas equation, PV = nRT assume one mole of gas ( n = 1) At STP, 10^5(Vo) = R(273)where Vo is the volume at STP But volume = mass/density hence, 10^5(m/po) = R(273) where m is the mass of gas and po is the density at STP At 800 kPa and 42'C (= 315 K), 8x10^5(V) = R(315) where V is the new volume i.e. 8x10^5(m/p) = R(315) where p is the new density Dividing the two equations: (p/po)(1/8) = 274/315 p = 8 x 273/315 x 1.25 kg/m^3 = 8.67 kg/m^2 3. Statement (1) is wrongAlthough there is cutting of field lines by both the sides AD and BC, you could, by using Fleming's right hand rule, find out that any induced current tends to flow from D to A and also from C to B. Thus these two currents cancel away and no net current is flowing. Be aware that the existence of induced emf in the coil doesn't not necessarily indicate that there is induced current. In this case, the induced emf on AD and BC are opposite in direction and would counter-balance one another, causing no current to flow. Statement (3): The coil rotates with AD as the axis of rotation. This is similar to, but not exactly the same as, what happens in a dynamo with a coil rotating in a magnetic field. There is change of magnetic flux linkage with the coil (or the side BC cuts through field lines). Hence, induced emf and current are produced.
其他解答:0D7DAC4E7B8CAAC5
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