Bài 30: Giải bài toán về hệ thấu kính
Hướng dẫn giải Bài 3 (Trang 195 SGK Vật lý 11)
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<p>3. Hai thấu kính, một hội tụ <span id="MathJax-Element-1-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mo stretchy="false">(</mo><msub><mi>f</mi><mn>1</mn></msub><mo>=</mo><mn>20</mn><mi>c</mi><mi>m</mi><mo stretchy="false">)</mo></math>"><span id="MJXc-Node-1" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-2" class="mjx-mrow"><span id="MJXc-Node-3" class="mjx-mo"></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>f</mi><mn>1</mn></msub><mo>=</mo><mn>20</mn><mo> </mo><mi>c</mi><mi>m</mi></math><math xmlns="http://www.w3.org/1998/Math/MathML"><mo stretchy="false"></mo></math></span>, một phân kỳ <span id="MathJax-Element-2-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mo stretchy="false">(</mo><msub><mi>f</mi><mn>2</mn></msub><mo>=</mo><mo>&#x2212;</mo><mn>10</mn><mi>c</mi><mi>m</mi><mo stretchy="false">)</mo></math>"><span id="MJXc-Node-12" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-13" class="mjx-mrow"><span id="MJXc-Node-14" class="mjx-mo"></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>f</mi><mn>2</mn></msub><mo>=</mo><mo>-</mo><mn>10</mn><mo> </mo><mi>c</mi><mi>m</mi></math><math xmlns="http://www.w3.org/1998/Math/MathML"><mo stretchy="false"></mo></math></span>, có cùng trục chính. Khoảng cách hai quang tâm là l = 30 cm. Vật AB vuông góc với trục chính được đặt bên trái <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>L</mi><mn>1</mn></msub></math> và cách <span id="MathJax-Element-4-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>L</mi><mn>1</mn></msub></math>"><span id="MJXc-Node-29" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-30" class="mjx-mrow"><span id="MJXc-Node-31" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-32" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>L</mi><mn>1</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span> một đoạn <span id="MathJax-Element-5-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>1</mn></msub></math>"><span id="MJXc-Node-34" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-35" class="mjx-mrow"><span id="MJXc-Node-36" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-37" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>1</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span>. </p>
<p>a) Cho <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>1</mn></msub><mo>=</mo><mn>20</mn><mo> </mo><mi>c</mi><mi>m</mi></math>, hãy xác định vị trí và tính số phóng đại ảnh cuối cùng cho bởi hệ hai thấu kính. Vẽ ảnh.</p>
<p>b) Tính <span id="MathJax-Element-7-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>1</mn></msub></math>"><span id="MJXc-Node-48" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-49" class="mjx-mrow"><span id="MJXc-Node-50" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-51" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>1</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span> để ảnh sau cùng là ảnh ảo và bằng hai lần vật.</p>
<p><strong>Giải</strong></p>
<p>Ta có: </p>
<h4>Câu a:</h4>
<p>Sơ đồ tạo ảnh qua hệ thấu kính:</p>
<p><img src="https://hoc247.net/images/fckeditor/upload/images/a1.PNG" alt="" /></p>
<p> Ta có: <math xmlns="http://www.w3.org/1998/Math/MathML"><mi></mi></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>1</mn></msub><mo>=</mo><mn>20</mn><mo> </mo><mi>c</mi><mi>m</mi><mo>,</mo><mo> </mo><msub><mi>f</mi><mn>1</mn></msub><mo>=</mo><mn>20</mn><mo> </mo><mi>c</mi><mi>m</mi><mo>,</mo><mo> </mo><mi>l</mi><mo>=</mo><mn>30</mn><mo> </mo><mi>c</mi><mi>m</mi><mspace linebreak="newline"/><mo>⇒</mo><msub><mi>d</mi><mn>1</mn></msub><mo>=</mo><mi>α</mi><mspace linebreak="newline"/><msub><mi>d</mi><mn>2</mn></msub><mo>=</mo><mi>l</mi><mo>-</mo><mi>d</mi><msub><mo>'</mo><mn>1</mn></msub><mo>=</mo><mo>-</mo><mi>α</mi><mspace linebreak="newline"/><mo>⇒</mo><mi>d</mi><msub><mo>'</mo><mn>2</mn></msub><mo>=</mo><msub><mi>f</mi><mn>2</mn></msub><mo>=</mo><mo>-</mo><mn>10</mn><mo> </mo><mi>c</mi><mi>m</mi></math></p>
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<p>Vẽ hình 30.2 SGK: <img src="https://hoc247.net/images/fckeditor/upload/images/a2.PNG" alt="Hệ hai thấu kính đồng trục ghép sát nhau" width="224" height="127" /></p>
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<p>Từ hình vẽ ta thấy: </p>
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<p>Vì <span id="MathJax-Element-13-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>1</mn></msub><msub><mi>B</mi><mn>1</mn></msub></math>"><span id="MJXc-Node-128" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-129" class="mjx-mrow"><span id="MJXc-Node-130" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-131" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>1</mn></msub><msub><mi>B</mi><mn>1</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span> ở vô cực nên chùm tia sáng từ AB tới qua tâm O1 sẽ qua <span id="MathJax-Element-14-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>1</mn></msub><msub><mi>B</mi><mn>1</mn></msub></math>"><span id="MJXc-Node-136" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-137" class="mjx-mrow"><span id="MJXc-Node-138" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-139" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>1</mn></msub><msub><mi>B</mi><mn>1</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span> và là chùm tia song song . Tương tự, chùm tia sáng từ <span id="MathJax-Element-15-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>1</mn></msub><msub><mi>B</mi><mn>1</mn></msub></math>"><span id="MJXc-Node-144" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-145" class="mjx-mrow"><span id="MJXc-Node-146" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-147" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>1</mn></msub><msub><mi>B</mi><mn>1</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span> tới qua tâm O2 sẽ qua <span id="MathJax-Element-16-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>2</mn></msub><msub><mi>B</mi><mn>2</mn></msub></math>"><span id="MJXc-Node-152" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-153" class="mjx-mrow"><span id="MJXc-Node-154" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-155" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>2</mn></msub><msub><mi>B</mi><mn>2</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span> cùng là chùm tia song song.</p>
<p>⇒ Tam giác <span id="MathJax-Element-17-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>A</mi><mi>B</mi><msub><mi>O</mi><mn>1</mn></msub></math>"><span id="MJXc-Node-160" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-161" class="mjx-mrow"><span id="MJXc-Node-162" class="mjx-mi"></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>A</mi><mi>B</mi><msub><mi>O</mi><mn>1</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span>đồng dạng với tam giác <span id="MathJax-Element-18-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>2</mn></msub><msub><mi>B</mi><mn>2</mn></msub><msub><mi>O</mi><mn>2</mn></msub></math>"><span id="MJXc-Node-167" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-168" class="mjx-mrow"><span id="MJXc-Node-169" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-170" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>2</mn></msub><msub><mi>B</mi><mn>2</mn></msub><msub><mi>O</mi><mn>2</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span> suy ra:</p>
<p><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>k</mi><mo>=</mo><mfrac><mrow><msub><mi>A</mi><mn>2</mn></msub><msub><mi>B</mi><mn>2</mn></msub></mrow><mrow><mi>A</mi><mi>B</mi></mrow></mfrac><mo>=</mo><mfrac><mrow><msub><mi>A</mi><mn>2</mn></msub><msub><mi>O</mi><mn>2</mn></msub></mrow><mrow><mi>A</mi><msub><mi>O</mi><mn>1</mn></msub></mrow></mfrac><mo>=</mo><mfrac><mfenced open="|" close="|"><mrow><mi>d</mi><msub><mo>'</mo><mn>2</mn></msub></mrow></mfenced><msub><mi>d</mi><mn>1</mn></msub></mfrac><mo>=</mo><mfrac><mfenced open="|" close="|"><mrow><mo>-</mo><mn>10</mn></mrow></mfenced><mn>20</mn></mfrac><mo>=</mo><mfrac><mn>1</mn><mn>2</mn></mfrac></math></p>
<h4>Câu b:</h4>
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<p>Ảnh <span id="MathJax-Element-20-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>2</mn></msub><msub><mi>B</mi><mn>2</mn></msub></math>"><span id="MJXc-Node-232" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-233" class="mjx-mrow"><span id="MJXc-Node-234" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-235" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>2</mn></msub><msub><mi>B</mi><mn>2</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span> là ảnh ảo và bằng hai lần vật. Ta có:</p>
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<p><math xmlns="http://www.w3.org/1998/Math/MathML"><mo>⇒</mo><mi>d</mi><msub><mo>'</mo><mn>1</mn></msub><mo>=</mo><mfrac><mrow><msub><mi>d</mi><mn>1</mn></msub><msub><mi>f</mi><mn>1</mn></msub></mrow><mrow><msub><mi>d</mi><mn>1</mn></msub><mo>-</mo><msub><mi>f</mi><mn>1</mn></msub></mrow></mfrac><mo>=</mo><mn>20</mn><mfrac><msub><mi>d</mi><mn>1</mn></msub><mrow><msub><mi>d</mi><mn>1</mn></msub><mo>-</mo><mn>20</mn></mrow></mfrac><mspace linebreak="newline"/><msub><mi>d</mi><mn>2</mn></msub><mo>=</mo><mn>1</mn><mo>-</mo><msub><mi>d</mi><mn>1</mn></msub><mo>⇒</mo><msub><mi>d</mi><mn>2</mn></msub><mo>=</mo><mn>30</mn><mspace linebreak="newline"/><mo>=</mo><mn>20</mn><mo>.</mo><mfrac><msub><mi>d</mi><mn>1</mn></msub><mrow><msub><mi>d</mi><mn>1</mn></msub><mo>-</mo><mn>20</mn></mrow></mfrac><mo>=</mo><mfrac><mrow><mn>10</mn><mo>.</mo><mo>(</mo><msub><mi>d</mi><mn>1</mn></msub><mo>-</mo><mn>60</mn><mo>)</mo></mrow><mrow><msub><mi>d</mi><mn>1</mn></msub><mo>-</mo><mn>20</mn></mrow></mfrac><mspace linebreak="newline"/><mo>⇒</mo><mfrac><mrow><mn>5</mn><mo>(</mo><mn>60</mn><mo>-</mo><msub><mi>d</mi><mn>1</mn></msub><mo>)</mo></mrow><mrow><msub><mi>d</mi><mn>1</mn></msub><mo>-</mo><mn>40</mn></mrow></mfrac><mo><</mo><mn>0</mn><mspace linebreak="newline"/><mo>⇒</mo><msub><mi>d</mi><mn>1</mn></msub><mo><</mo><mn>40</mn><mo> </mo><mi>c</mi><mi>m</mi><mo> </mo></math></p>
<p>và <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>2</mn></msub><mo>></mo><mn>60</mn><mo> </mo><mi>c</mi><mi>m</mi></math></p>
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<p>Ảnh <span id="MathJax-Element-27-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>2</mn></msub><msub><mi>B</mi><mn>2</mn></msub></math>"><span id="MJXc-Node-367" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-368" class="mjx-mrow"><span id="MJXc-Node-369" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-370" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>A</mi><mn>2</mn></msub><msub><mi>B</mi><mn>2</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span> là ảnh ảo và bằng hai lần vật AB:</p>
</li>
</ul>
<p><span id="MathJax-Element-28-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>k</mi><mo>=</mo><mrow><mo>(</mo><mrow><mo>&#x2212;</mo><mfrac><msub><mi>d</mi><mn>1</mn></msub><msub><mi>d</mi><mn>1</mn></msub></mfrac></mrow><mo>)</mo></mrow><mo>.</mo><mrow><mo>(</mo><mrow><mo>&#x2212;</mo><mfrac><msub><mi>d</mi><mn>2</mn></msub><msub><mi>d</mi><mn>2</mn></msub></mfrac></mrow><mo>)</mo></mrow><mo>=</mo><mfrac><mrow><msub><mi>d</mi><mn>1</mn></msub><mo>.</mo><msub><mi>d</mi><mn>2</mn></msub></mrow><mrow><msub><mi>d</mi><mn>1</mn></msub><mo>.</mo><msub><mi>d</mi><mn>2</mn></msub></mrow></mfrac></math>"><span id="MJXc-Node-375" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-376" class="mjx-mrow"><span id="MJXc-Node-377" class="mjx-mi"></span></span></span></span></p>
<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>k</mi><mo>=</mo><mo>(</mo><mo>-</mo><mfrac><msub><mi>d</mi><mn>1</mn></msub><msub><mi>d</mi><mn>1</mn></msub></mfrac><mo>)</mo><mo>.</mo><mo>(</mo><mo>-</mo><mfrac><msub><mi>d</mi><mn>2</mn></msub><msub><mi>d</mi><mn>2</mn></msub></mfrac><mo>)</mo><mo>=</mo><mfrac><mrow><msub><mi>d</mi><mn>1</mn></msub><msub><mi>d</mi><mn>2</mn></msub></mrow><mrow><msub><mi>d</mi><mn>1</mn></msub><msub><mi>d</mi><mn>2</mn></msub></mrow></mfrac><mspace linebreak="newline"/><mo>=</mo><mfrac><mn>10</mn><mrow><msub><mi>d</mi><mn>1</mn></msub><mo>-</mo><mn>40</mn></mrow></mfrac><mo>=</mo><mo>±</mo><mn>2</mn><mspace linebreak="newline"/><mo>⇒</mo><mi>k</mi><mo>=</mo><mo>±</mo><mn>2</mn><mo>=</mo><mfrac><mn>20</mn><mrow><msub><mi>d</mi><mn>1</mn></msub><mo>-</mo><mn>60</mn></mrow></mfrac><mo> </mo><mo> </mo><mo> </mo><mo>(</mo><mo>*</mo><mo>)</mo></math> </div>
<div class="i-content content-fck">
<ul>
<li>
<p>Giải phương trình (*) ra ta được: <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>1</mn></msub></math>=35cm ( nhận) và <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>1</mn></msub></math> =45cm (loại)</p>
</li>
</ul>
<h4>Đáp số:</h4>
<p>a. <span id="MathJax-Element-32-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msubsup><mi>d</mi><mn>2</mn><mo>&#x2032;</mo></msubsup><mo>=</mo><msub><mi>f</mi><mn>2</mn></msub><mo>=</mo><mo>&#x2212;</mo><mn>10</mn><mi>c</mi><mi>m</mi></math>"><span id="MJXc-Node-460" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-461" class="mjx-mrow"><span id="MJXc-Node-462" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-463" class="mjx-mi"></span></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>d</mi><msub><mo>'</mo><mn>2</mn></msub><mo>=</mo><msub><mi>f</mi><mn>2</mn></msub><mo>=</mo><mo>-</mo><mn>10</mn><mo> </mo><mi>c</mi><mi>m</mi></math> và <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>k</mi><mo>=</mo><mfrac><mn>1</mn><mn>2</mn></mfrac></math><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn></mn></mfrac></math></p>
<p>b. <span id="MathJax-Element-34-Frame" class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 18.08px; letter-spacing: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>1</mn></msub></math>"><span id="MJXc-Node-482" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-483" class="mjx-mrow"><span id="MJXc-Node-484" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-485" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>1</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span>=35cm </p>
</div>
</div>
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Hướng Dẫn Giải Bài 3 ( Trang 195 - SGK Vật Lí 11)
GV: 
GV colearn
GV colearn
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Hướng Dẫn Giải Bài 3 ( Trang 195 - SGK Vật Lí 11)
GV: GV colearn
GV colearn