The correct answer is B because:

For a filament lamp, current and potential difference are not directly proportional
Hence, the I-V graph will not show a straight line
- This eliminates options A and C
The resistance of the filament lamp increases as the temperature of the filament increases
- The gradient of an I-V graph represents the resistance
Consider the change in gradient that would represent an increase in resistance:
- According to Ohm's Law: $V = I R$
- So, $R = \frac{V}{I}$
- Hence, $r e s i s t a n c e = \frac{1}{g r a d i e n t}$
- So, a decrease in gradient would represent an increase in resistance
Compare the change in resistance of options B and D
- By drawing tangents to both curves at two points

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Simple Circuits (OCR Gateway GCSE Physics: Combined Science)

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