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Student & Learning Zone - City & Guilds
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<blockquote data-quote="SPECIAL LOCATION" data-source="post: 113532" data-attributes="member: 250"><p>Right Majid....</p><p></p><p>I think you have written your question down slightly wrong...</p><p></p><p>I reckon the line about the 0.5amps should be the current through the parallel 20ohm resistor.</p><p></p><p>as the current through the two parallel resistors will be different if resistances are different.</p><p></p><p><em><strong>Remember</strong></em></p><p></p><p>Resistors in series: Voltage divides, Current stays constant.</p><p></p><p>Resistors in parallel: Voltage stays constant, Current divides.</p><p></p><p>So:-</p><p></p><p>If 0.5a through the 20ohm resistor IxR=V 0.5A x 20ohm = 10V</p><p></p><p>If 10 of our volts are across the parallel resistors then the remaining 20v</p><p></p><p>(30v -10v), must be across the 5ohm resistor.</p><p></p><p>20V / 5ohm = 4A.</p><p></p><p>So 4amps total drawn by circuit,</p><p></p><p>0.5A is going down the 20ohm parallel path</p><p></p><p>so (4A - 0.5A) 3.5A are going through the unknown resistor.</p><p></p><p>And</p><p></p><p>the unknown resistor has 10V across it.</p><p></p><p>R = V/I 10v / 3.5A = 2.857ohms.</p><p></p><p>Therefore...</p><p></p><p><strong>Unknown resistor equals 2.86 ohms!</strong></p><p></p><p> <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite8" alt=":D" title="Big grin :D" loading="lazy" data-shortname=":D" /> </p><p></p><p>coffeeput the kettle on</p></blockquote><p></p>
[QUOTE="SPECIAL LOCATION, post: 113532, member: 250"] Right Majid.... I think you have written your question down slightly wrong... I reckon the line about the 0.5amps should be the current through the parallel 20ohm resistor. as the current through the two parallel resistors will be different if resistances are different. [I][B]Remember[/B][/I] Resistors in series: Voltage divides, Current stays constant. Resistors in parallel: Voltage stays constant, Current divides. So:- If 0.5a through the 20ohm resistor IxR=V 0.5A x 20ohm = 10V If 10 of our volts are across the parallel resistors then the remaining 20v (30v -10v), must be across the 5ohm resistor. 20V / 5ohm = 4A. So 4amps total drawn by circuit, 0.5A is going down the 20ohm parallel path so (4A - 0.5A) 3.5A are going through the unknown resistor. And the unknown resistor has 10V across it. R = V/I 10v / 3.5A = 2.857ohms. Therefore... [B]Unknown resistor equals 2.86 ohms![/B] :D coffeeput the kettle on [/QUOTE]
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