<p>In an experiment to investigate the relationship between light intensity \(I\) lux on a surface and distance \(d\) metres from a light source, a student obtained the following results. One of the values of \(I\) is incorrect.</p>
<div class="content-block content-block--table"><div class="table-container"><table style="width: 100%;"><thead><tr><th style="text-align: left; --cell-justify: flex-start">\(d\) (metres)</th><th style="text-align: left; --cell-justify: flex-start">\(2\)</th><th style="text-align: left; --cell-justify: flex-start">\(5\)</th><th style="text-align: left; --cell-justify: flex-start">\(10\)</th><th style="text-align: left; --cell-justify: flex-start">\(20\)</th><th style="text-align: left; --cell-justify: flex-start">\(30\)</th></tr></thead><tbody><tr><td style="text-align: left; --cell-justify: flex-start">\(I\) (lux)</td><td style="text-align: left; --cell-justify: flex-start">\(875\)</td><td style="text-align: left; --cell-justify: flex-start">\(141\)</td><td style="text-align: left; --cell-justify: flex-start">\(35\)</td><td style="text-align: left; --cell-justify: flex-start">\(4.22\)</td><td style="text-align: left; --cell-justify: flex-start">\(3.89\)</td></tr></tbody></table></div></div>
<p>It is known that&nbsp;\(I\) and \(d\) are related by the equation \(I = Ad^n\), where&nbsp;\(A\) and \(n\) are constants.</p>
<ol class="abc-list"><li><div class="list-item-content"><span class="list-item-text">Plot \(\lg I\) against \(\lg d\) and draw a straight line graph.</span><span class="inline-marks">[3]</span></div></li><li><div class="list-item-content"><span class="list-item-text">Use your graph to</span></div><ol class="i-list"><li><div class="list-item-content"><span class="list-item-text">identify the incorrect reading of \(I\) and estimate its correct value,</span><span class="inline-marks">[3]</span></div></li><li><div class="list-item-paragraph">estimate the value of A and of n.<span class="inline-marks">[4]</span></div></li></ol></li><li><div class="list-item-paragraph">Using the tables of values, explain, with working, how the light intensity <em>I</em> changes when the distance <em>d</em> from the light source is doubled.<span class="inline-marks">[1]</span></div></li></ol>

In an experiment to investigate the relationship between light intensity \(I\) lux on a surface and distance \(d\) metres from a light source, a student obtained the following results. One of the values of \(I\) is incorrect.

It is known that \(I\) and \(d\) are related by the equation \(I = Ad^n\), where \(A\) and \(n\) are constants.

Plot \(\lg I\) against \(\lg d\) and draw a straight line graph.

identify the incorrect reading of \(I\) and estimate its correct value,

Using the tables of values, explain, with working, how the light intensity *I* changes when the distance *d* from the light source is doubled.

2025 SJI PRELIMS P2 Q7

2025 SJI PRELIMS P2 Q7