Ngā Tauira Pātai e Matapaki ana i te Kaha Hiko Whakaoho (EMF)
Ko te kaha hiko whakaawe (EMF) he ariā taketake i roto i te hiko aukume, ā, he kaupapa matua i roto i ngā akoranga ahupūngao, i te kura tuarua me te whare wānanga. He mea nui te mārama ki te emf whakaawe nā te mea he whānuitia ōna whakamahinga i roto i ngā hangarau hou, pērā i ngā whakaputa hiko, ngā whakawhiti hiko, me ētahi atu taputapu hiko. I roto i tēnei tuhinga, ka matapakihia e mātou ētahi tauira raruraru me ā rātou otinga e pā ana ki te emf whakaawe hei whakahōhonu ake i tō tātou māramatanga ki tēnei ariā.
He Kupu Whakataki ki te EMF Whakaoho
I mua i te ruku hohonu ki te tauira raruraru, me mārama tuatahi tātou ki te ariā taketake o te emf whakaoho. Ko te emf whakaoho ko te kaha hiko e puta mai ana i te huringa o te rerenga aukume i roto i te ara iahiko. I kitea tuatahitia tēnei āhuatanga e Michael Faraday, nō reira te ingoa ko te Ture a Faraday. I roto i te pāngarau, ko te Ture a Faraday te kī:
\[ \mathcal{E} = -\frac{d\Phi}{dt} \]
Kei hea:
– Ko te EMF (Volts) i whakaohokia e \(\mathcal{E}\)
– Ko te rerenga aukume (Weber) te \(\Phi\)
– Ko te huringa o te rerenga aukume ko te \(d\Phi\)
– Ko te huringa o te wā ko te \(dt\)
Ko te Ture a Lenz e whakamārama ana i te tohu kino i roto i te whārite, e kī ana ko te ahunga o te EMF whakaoho he rite tonu ki te ātete ki te huringa o te rerenga aukume e hua ai.
Kia mārama tātou ki ngā kaupapa matua o tēnei ariā, me tahuri tātou ki ngā tauira pātai me ngā matapakinga mō aua pātai.
Tauira Pātai 1
Pātai:
E 200 ngā hurihanga o tētahi koiri, ā, ka whakanohoia ki roto i tētahi papa aukume ōrite me te rahi o te papa aukume o \( B = 0,5 \) Tesla. Mena he 0,1 m² te horahanga whakawhiti-wāhanga o te koiri, tatauhia te EMF whakaoho i puta mai mena ka hurihia te papa aukume i runga i te koiri mai i te 0,5 T ki te 0 i roto i te 0,02 hēkona.
Kōrero:
Tuatahi, ka tatauhia e mātou te huringa o te rerenga aukume (\( \Delta \Phi \)):
\[
\Delta \Phi = N \cdot \Delta (B \cdot A)
\]
Kei hea:
– \( N = 200 \) (te maha o ngā takahuri)
– Ka huri te \( B \) mai i te 0,5 T ki te 0 T (nō reira \( \Delta B = 0 – 0,5 = -0,5 \) T)
– \( A = 0,1 \) m²
Nō reira:
\[
\Delta \Phi = 200 \cdot (-0,5 \cdot 0,1) = 200 \cdot (-0,05) = -10 \text{ Weber}
\]
Muri iho, ka tatauhia e mātou te EMF i whakaohokia (\( \mathcal{E} \)):
\[
\mathcal{E} = -\frac{\Delta \Phi}{\Delta t}
\]
Ko \( \Delta t = 0,02 \) hēkona, nō reira:
\[
\mathcal{E} = -\frac{-10}{0,02} = 500 \text{ Ngā Āhuatanga Pūngao}
\]
Nō reira, ko te EMF whakaoho i whakaputaina he 500 Volts.
Tauira Pātai 2
Pātai:
Ka whakanohoia he mowhiti whakarewa he 10 cm te whānui ki roto i tētahi papa aukume e huri ana i te tere o te \(0,1 \) Tesla ia hekona. Tātaihia te emf whakaoho i puta i roto i te mowhiti.
Kōrero:
Hei tatau i te EMF whakaoho, ka whakamahia e mātou te Ture a Faraday, ā, ka tīmata mātou mā te tatau i te rerenga aukume:
\[
\Delta \Phi = \Delta B \cdot A
\]
Ko te horahanga whakawhiti-wāhanga o te mowhiti (\( A \)) ko:
\[
A = \pi r^2 = \pi \left(\frac{d}{2}\right)^2 = \pi \left(\frac{0,1}{2}\right)^2 = \frac{\pi}{400} \text{ m}^2
\]
Me te tere o te huringa o te papa aukume \(\Delta B = 0,1\) T/hēkona:
\[
\mathcal{E} = -N \frac{d \Phi}{dt} = -N \cdot \frac{\Delta B \cdot A}{\Delta t}
\]
Nā te mea he pumau te tere o te huringa o \( \Delta t \), \( N =1\) me whakakapi ngā uara:
\[
\mathcal{E} = – 1 \cdot \left( 0,1 \cdot \frac{\pi}{400} \right) = – \frac{\pi}{4000} \text{ Ngāohiko}
\]
Nō reira, ko te EMF whakaoho i puta i roto i te mowhiti ko \(\frac{\pi}{4000} \text{ Volt} \approx 0,000785 \text{ Volt}\).
Tauira Pātai 3
Pātai:
E neke poutū ana tētahi kaiārahi tika, 1 mita te roa, i te tere o te 5 m/s i roto i tētahi papa aukume ōrite o te 0,2 T. He aha te EMF e whakaohokia ana i roto i te kaiārahi?
Kōrero:
Hei whiwhi i te EMF i puta mai i roto i te kaiārahi neke, ka whakamahia e mātou te tātai:
\[
\mathcal{E} = B \cdot l \cdot v
\]
Kei hea:
– \( B = 0,2 \) T
– \( l = 1 \) m
– \( v = 5 \) m/s
Whakakapia ēnei uara ki roto i te tātai:
\[
\mathcal{E} = 0,2 \times 1 \times 5 = 1 \text{ Ngāohiko}
\]
Nō reira, ko te EMF whakaoho i hangaia i roto i te ara iahiko he 1 Volt.
Whakamutunga
He mea nui te mārama ki te kaha hiko whakaaweawe (EMF) me te Ture a Faraday i roto i te ahupūngao, inā koa i roto i te horopaki o te hikohiko. E whakaatu ana ngā tauira i runga ake nei i ngā whakamahinga rerekē o tēnei ariā, tae atu ki te whakarerekētanga o ngā papa aukume, ngā kaiārahi neke, me ētahi atu whakamahinga. Mā te mōhio ki ngā tikanga tatau mō ngā whirihoranga ara iahiko me ngā āhuatanga o te papa aukume ka hohonu ake tō tātou māramatanga ki tēnei ariā, ā, ka taea hoki te whakamahi ki ngā hangarau hou.
