Bài 30: Giải bài toán về hệ thấu kính
Hướng dẫn giải Bài 2 (Trang 195 SGK Vật lý 11)
<p>2. Tiếp theo các giả thiết cho ở bài tập 1.</p>
<p>Đặt giữa <span class="MathJax_Preview"><span id="MJXp-Span-1" class="MJXp-math"><span id="MJXp-Span-2" class="MJXp-msubsup"><span id="MJXp-Span-3" class="MJXp-mi MJXp-italic"></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>L</mi><mn>1</mn></msub></math><span id="MJXp-Span-4" class="MJXp-mn MJXp-script"></span></span></span></span> và H một thấu kính hội tụ <span class="MathJax_Preview"><span id="MJXp-Span-5" class="MJXp-math"><span id="MJXp-Span-6" class="MJXp-msubsup"><span id="MJXp-Span-7" class="MJXp-mi MJXp-italic"></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>L</mi><mn>2</mn></msub></math><span id="MJXp-Span-8" class="MJXp-mn MJXp-script"></span></span></span></span>. Khi xê dịch <span class="MathJax_Preview"><span id="MJXp-Span-9" class="MJXp-math"><span id="MJXp-Span-10" class="MJXp-msubsup"><span id="MJXp-Span-11" class="MJXp-mi MJXp-italic"></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>L</mi><mn>2</mn></msub></math><span id="MJXp-Span-12" class="MJXp-mn MJXp-script"></span></span></span></span>, học sinh này nhận thấy chỉ có một vị trí duy nhất của <span class="MathJax_Preview"><span id="MJXp-Span-13" class="MJXp-math"><span id="MJXp-Span-14" class="MJXp-msubsup"><span id="MJXp-Span-15" class="MJXp-mi MJXp-italic"></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>L</mi><mn>2</mn></msub></math><span id="MJXp-Span-16" class="MJXp-mn MJXp-script"></span></span></span></span> tạo được điểm sáng tại H.</p>
<p>Tiêu cự của <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>L</mi><mn>2</mn></msub></math><span class="MathJax_Preview"><span id="MJXp-Span-17" class="MJXp-math"><span id="MJXp-Span-18" class="MJXp-msubsup"><span id="MJXp-Span-20" class="MJXp-mn MJXp-script"></span></span></span></span> là bao nhiêu ?</p>
<p>A. 10 cm.</p>
<p>B. 15 cm.</p>
<p>C. 20 cm.</p>
<p>D. Một giá trị khác A, B, C.</p>
<p><strong>Giải</strong></p>
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<p>Ta có: </p>
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<p>Sơ đồ tạo ảnh qua hệ thấu kính:</p>
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</ul>
<p><img src="https://hoc247.net/images/fckeditor/upload/images/a1.PNG" alt="" /></p>
<ul>
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<p>Trong đó:</p>
</li>
</ul>
<p> <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>d</mi><mn>1</mn></msub><mo>=</mo><mi>α</mi><mo>⇒</mo><mi>d</mi><msub><mo>'</mo><mn>1</mn></msub><mo>=</mo><msub><mi>f</mi><mn>1</mn></msub><mo>=</mo><mo>-</mo><mn>10</mn><mi>c</mi><mi>m</mi><mspace linebreak="newline"/><mo>→</mo><msub><mi>d</mi><mn>2</mn></msub><mo>=</mo><msub><mi>O</mi><mn>1</mn></msub><msub><mi>O</mi><mn>2</mn></msub><mo>-</mo><mi>d</mi><msub><mo>'</mo><mn>1</mn></msub><mo>=</mo><mi>a</mi><mo>-</mo><mo>(</mo><mo>-</mo><mn>10</mn><mo>)</mo><mo>=</mo><mi>a</mi><mo>+</mo><mn>10</mn></math><span id="MathJax-Element-8-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><mo>=&#x221D;&#x21D2;</mo><msubsup><mi>d</mi><mn>1</mn><mo>&#x2032;</mo></msubsup><mo>=</mo><msub><mi>f</mi><mn>1</mn></msub><mo>=</mo><mo>&#x2212;</mo><mn>10</mn><mi>c</mi><mi>m</mi></math>"><span id="MJXc-Node-36" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-37" class="mjx-mrow"><span id="MJXc-Node-38" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-39" class="mjx-mi"></span></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><mn></mn></math></p>
<ul>
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<p>Điều kiện để chỉ có một vị trí duy nhất của <span id="MathJax-Element-10-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>2</mn></msub></math>"><span id="MJXc-Node-84" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-85" class="mjx-mrow"><span id="MJXc-Node-86" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-87" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I">L</span></span></span><span class="mjx-sub"><span id="MJXc-Node-88" class="mjx-mn"><span class="mjx-char MJXc-TeX-main-R">2</span></span></span></span></span></span><span class="MJX_Assistive_MathML" role="presentation"><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>L</mi><mn>2</mn></msub></math></span></span> tạo được điểm sáng tại H là: </p>
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</ul>
<p><math xmlns="http://www.w3.org/1998/Math/MathML"><mi>d</mi><msub><mo>'</mo><mn>2</mn></msub><mo>=</mo><msub><mi>d</mi><mn>2</mn></msub><mo>;</mo><mo> </mo><mi>d</mi><msub><mo>'</mo><mn>2</mn></msub><mo>+</mo><msub><mi>d</mi><mn>2</mn></msub><mo>=</mo><msub><mi>S</mi><mn>1</mn></msub><mi>H</mi><mo>=</mo><mn>80</mn><mi>c</mi><mi>m</mi><mspace linebreak="newline"/><mo>⇒</mo><mi>d</mi><msub><mo>'</mo><mn>2</mn></msub><mo>=</mo><msub><mi>d</mi><mn>2</mn></msub><mo>=</mo><mn>40</mn><mi>c</mi><mi>m</mi><mo>.</mo></math></p>
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<p>Tiêu cự của <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>L</mi><mn>2</mn></msub></math>"><span id="MJXc-Node-132" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-133" class="mjx-mrow"><span id="MJXc-Node-134" class="mjx-msubsup"><span class="mjx-base"><span id="MJXc-Node-135" class="mjx-mi"></span></span></span></span></span><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>L</mi><mn>2</mn></msub></math><math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mn></mn></msub></math></span> là: <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-table; 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>f</mi><mo>=</mo><mfrac><mrow><msubsup><mi>d</mi><mn>2</mn><mo>&#x2032;</mo></msubsup><msub><mi>d</mi><mn>2</mn></msub></mrow><mrow><msubsup><mi>d</mi><mn>2</mn><mo>&#x2032;</mo></msubsup><mo>+</mo><msub><mi>d</mi><mn>2</mn></msub></mrow></mfrac><mo>=</mo><mn>20</mn><mi>c</mi><mi>m</mi></math>"><span id="MJXc-Node-137" class="mjx-math" aria-hidden="true"><span id="MJXc-Node-138" class="mjx-mrow"><span id="MJXc-Node-139" class="mjx-mi"><span class="mjx-char MJXc-TeX-math-I">f<math xmlns="http://www.w3.org/1998/Math/MathML"><mo>=</mo><mfrac><mrow><mi>d</mi><msub><mo>'</mo><mn>2</mn></msub><msub><mi>d</mi><mn>2</mn></msub></mrow><mrow><mi>d</mi><msub><mo>'</mo><mn>2</mn></msub><mo>+</mo><msub><mi>d</mi><mn>2</mn></msub></mrow></mfrac><mo>=</mo><mn>20</mn><mo> </mo><mi>c</mi><mi>m</mi></math></span></span><span id="MJXc-Node-140" class="mjx-mo MJXc-space3"></span></span></span></span></p>
</li>
</ul>
<p><span class="mjx-chtml MathJax_CHTML" style="box-sizing: border-box; margin: 0px; padding: 1px 0px; overflow-wrap: normal; word-break: break-word; display: inline-table; 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>f</mi><mo>=</mo><mfrac><mrow><msubsup><mi>d</mi><mn>2</mn><mo>&#x2032;</mo></msubsup><msub><mi>d</mi><mn>2</mn></msub></mrow><mrow><msubsup><mi>d</mi><mn>2</mn><mo>&#x2032;</mo></msubsup><mo>+</mo><msub><mi>d</mi><mn>2</mn></msub></mrow></mfrac><mo>=</mo><mn>20</mn><mi>c</mi><mi>m</mi></math>">⇒ Đáp án C </span></p>
Hướng Dẫn Giải Bài 2 ( Trang 195 - SGK Vật Lí 11)
GV: 
GV colearn
GV colearn
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Hướng Dẫn Giải Bài 2 ( Trang 195 - SGK Vật Lí 11)
GV: GV colearn
GV colearn