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PHYSICS ISA ON LDRs.. watch

1. Hi ,

So I have my Physics ISA Paper 1 next week and I think I have an explanation for my hypothesis>>

The resistance of the LDR decrease as the light intensity increases since the increased intensity induces more electrons in the current, hence more charge can be carried. According to Ohms Law, as the current increases, the resistance must decrease.

^ Is this fine \ is there anything else that I need to add \ is it completely incorrect..

pt.2 Could someone recommend an experiment to test this hypothesis? Thanks!
2. (Original post by ||TheUnknown||)
Hi ,

So I have my Physics ISA Paper 1 next week and I think I have an explanation for my hypothesis>>

The resistance of the LDR decrease as the light intensity increases since the increased intensity induces more electrons in the current, hence more charge can be carried. According to Ohms Law, as the current increases, the resistance must decrease.

^ Is this fine \ is there anything else that I need to add \ is it completely incorrect..
Hmmmmm.

Your understanding lacks some fundamental concepts:

'The resistance of the LDR decrease as the light intensity increases' correct.

'since the increased intensity induces more electrons in the current' No. The reduction in resistance allows more current (electrons) to flow through the LDR in accordance with ohms law.

'According to Ohms Law, as the current increases, the resistance must decrease' No. Wrong way around. As the resistance decreases, the current increases.

In the context of an LDR, changing the light intensity falling on the LDR causes a change in it's resistance.

Any EMF (voltage) placed across the LDR by an external power source, will cause an electron flow of current through the LDR. The current flow is limited by the resistance of the LDR and obeys ohms law for any given value of resistance. The external supply remains constant so according to ohms law, as the LDR resistance changes dependent on the light intensity falling on it, the current through the LDR must change accordingly.
3. (Original post by uberteknik)
Hmmmmm.

Your understanding lacks some fundamental concepts:

'The resistance of the LDR decrease as the light intensity increases' correct.

'since the increased intensity induces more electrons in the current' No. The reduction in resistance allows more current (electrons) to flow through the LDR in accordance with ohms law.

'According to Ohms Law, as the current increases, the resistance must decrease' No. Wrong way around. As the resistance decreases, the current increases.

In the context of an LDR, changing the light intensity falling on the LDR causes a change in it's resistance.

Any EMF (voltage) placed across the LDR by an external power source, will cause an electron flow of current through the LDR. The current flow is limited by the resistance of the LDR and obeys ohms law for any given value of resistance. The external supply remains constant so according to ohms law, as the LDR resistance changes dependent on the light intensity falling on it, the current through the LDR must change accordingly.
Thank you so much but there is one thing that I still am confused about> why the resistance decreases as the light intensity increases. I understand that the current flowing through is limited by the resistance of the LDR but I am not sure about why the resistance changes..

Thanks again
4. (Original post by ||TheUnknown||)
Thank you so much but there is one thing that I still am confused about> why the resistance decreases as the light intensity increases. I understand that the current flowing through is limited by the resistance of the LDR but I am not sure about why the resistance changes..

Thanks again
LDR's are fabricated from a semiconducting element.

At GCSE level you are not expected to know how LDR's perform the way they do which requires an understanding of the photoelectric effect and quantum mechanics.

Your GCSE experiment cannot possibly produce enough observation and evidence to suggest a conclusion to how an LDR works at the sub-atomic level.
5. (Original post by uberteknik)
LDR's are fabricated from a semiconducting element.

At GCSE level you are not expected to know how LDR's perform the way the do which requires an understanding of the photoelectric effect and quantum mechanics.

Your GCSE experiment cannot possibly produce enough observation and evidence to suggest a conclusion to how an LDR works at the sub-atomic level.
Oh! Thank you very much

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