Bài 45: Ảnh của một vật tạo bởi thấu kính phân kì
Hướng dẫn Giải Câu hỏi 7 (Trang 123 SGK Vật lý lớp 9 )
<p>Vận dụng kiến thức học, tính khoảng cách từ ảnh đến thấu kính và chiều cao của ảnh trong hai trường hợp ở C5 khi vật có chiều cao h = 6mm</p>
<p>Giải</p>
<p>Đã cho: OF = OF' =f = 12cm</p>
<p><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span>OA = d = 8cm</p>
<p><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span>AB = h = 6mm = 0,6cm</p>
<p>Cần tìm: A'B' =h' = ?</p>
<p><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span>OA' = d' = ?</p>
<ul>
<li>Hình a(trang 140): đối với thấu kính hội tụ.</li>
</ul>
<p>Xét <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>△</mo><mi>B</mi><mi>B</mi><mo>'</mo><mi>I</mi><mo> </mo><mo>∾</mo><mo>△</mo><mi>O</mi><mi>B</mi><mo>'</mo><mi>F</mi><mo>'</mo></math> có </p>
<p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mi>B</mi><mi>I</mi></mrow><mrow><mi>O</mi><mi>F</mi><mo>'</mo></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mi>B</mi><mi>B</mi><mo>'</mo></mrow><mrow><mi>O</mi><mi>B</mi><mo>'</mo></mrow></mfrac><mo> </mo><mo>⇔</mo><mfrac><mrow><mi>A</mi><mi>O</mi></mrow><mrow><mi>O</mi><mi>F</mi><mo>'</mo></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mi>B</mi><mi>B</mi><mo>'</mo></mrow><mrow><mi>O</mi><mi>B</mi><mo>'</mo></mrow></mfrac><mspace linebreak="newline"/><mo>⇒</mo><mi>O</mi><mi>B</mi><mo>'</mo><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mi>O</mi><mi>F</mi><mo>'</mo><mo>.</mo><mi>B</mi><mi>B</mi><mo>'</mo></mrow><mrow><mi>A</mi><mi>O</mi></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mn>12</mn><mo>.</mo><mi>B</mi><mi>B</mi><mo>'</mo></mrow><mn>8</mn></mfrac><mo> </mo><mo>=</mo><mo> </mo><mn>1</mn><mo>,</mo><mn>5</mn><mi>B</mi><mi>B</mi><mo>'</mo><mspace linebreak="newline"/></math></p>
<p>Xét <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>△</mo><mi>O</mi><mi>A</mi><mi>B</mi><mo> </mo><mo>∾</mo><mo>△</mo><mi>O</mi><mi>A</mi><mo>'</mo><mi>B</mi><mo>'</mo></math> có:</p>
<p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mi>O</mi><mi>A</mi></mrow><mrow><mi>O</mi><mi>A</mi><mo>'</mo></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mi>O</mi><mi>B</mi></mrow><mrow><mi>O</mi><mi>B</mi><mo>'</mo></mrow></mfrac><mo> </mo><mo>⇔</mo><mfrac><mrow><mi>O</mi><mi>A</mi></mrow><mrow><mi>O</mi><mi>A</mi><mo>'</mo></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mi>O</mi><mi>B</mi><mo>'</mo><mo> </mo><mo>-</mo><mo> </mo><mi>B</mi><mi>B</mi><mo>'</mo></mrow><mrow><mi>O</mi><mi>B</mi><mo>'</mo></mrow></mfrac><mo>=</mo><mfrac><mrow><mn>1</mn><mo>,</mo><mn>5</mn><mi>B</mi><mi>B</mi><mo>'</mo><mo>-</mo><mi>B</mi><mi>B</mi><mo>'</mo></mrow><mrow><mn>1</mn><mo>,</mo><mn>5</mn><mi>B</mi><mi>B</mi><mo>'</mo></mrow></mfrac><mo>=</mo><mfrac><mn>1</mn><mn>3</mn></mfrac><mspace linebreak="newline"/></math></p>
<p><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span> <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>⇒</mo><mo> </mo><mi>O</mi><mi>A</mi><mo>'</mo><mo> </mo><mo>=</mo><mo> </mo><mn>3</mn><mi>O</mi><mi>A</mi><mo> </mo><mo>=</mo><mo> </mo><mn>3</mn><mo>.</mo><mn>8</mn><mo> </mo><mo>=</mo><mo> </mo><mn>24</mn><mo> </mo><mo>(</mo><mi>c</mi><mi>m</mi><mo>)</mo></math><span class="mce-nbsp-wrap" contenteditable="false"> </span></p>
<p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mi>O</mi><mi>A</mi></mrow><mrow><mi>O</mi><mi>A</mi><mo>'</mo></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mi>A</mi><mi>B</mi></mrow><mrow><mi>A</mi><mo>'</mo><mi>B</mi><mo>'</mo></mrow></mfrac><mo> </mo><mo>⇒</mo><mi>A</mi><mo>'</mo><mi>B</mi><mo>'</mo><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mi>O</mi><mi>A</mi><mo>'</mo><mo>.</mo><mi>A</mi><mi>B</mi></mrow><mrow><mi>O</mi><mi>A</mi></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mn>24</mn><mo>.</mo><mn>0</mn><mo>,</mo><mn>6</mn></mrow><mn>8</mn></mfrac><mo> </mo><mo>=</mo><mo> </mo><mn>1</mn><mo>,</mo><mn>8</mn><mo> </mo><mo>(</mo><mi>c</mi><mi>m</mi><mo>)</mo></math></p>
<p>Đáp số: OA' = d' = 24cm</p>
<p><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span>A'B' = h' = 1,8cm</p>
<ul>
<li>Hình b (trang 140): Đối với thấu kính phân kì.</li>
</ul>
<p>Xét <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>△</mo><mi>B</mi><mi>I</mi><mi>B</mi><mo>'</mo><mo> </mo><mo>∾</mo><mo>△</mo><mi>O</mi><mi>F</mi><mo>'</mo><mi>B</mi><mo>'</mo></math> có:</p>
<p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mi>B</mi><mi>I</mi></mrow><mrow><mi>O</mi><mi>F</mi><mo>'</mo></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mi>B</mi><mi>B</mi><mo>'</mo></mrow><mrow><mi>O</mi><mi>B</mi><mo>'</mo></mrow></mfrac><mo> </mo><mo>⇒</mo><mi>O</mi><mi>B</mi><mo>'</mo><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mi>O</mi><mi>F</mi><mo>'</mo><mo>.</mo><mi>B</mi><mi>B</mi><mo>'</mo></mrow><mrow><mi>A</mi><mi>O</mi></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mn>12</mn><mo>.</mo><mi>B</mi><mi>B</mi><mo>'</mo></mrow><mn>8</mn></mfrac><mo> </mo><mo>=</mo><mo> </mo><mn>1</mn><mo>,</mo><mn>5</mn><mi>B</mi><mi>B</mi><mo>'</mo></math></p>
<p>Xét <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>△</mo><mi>O</mi><mi>A</mi><mo>'</mo><mi>B</mi><mo>'</mo><mo> </mo><mo>∾</mo><mo>△</mo><mi>O</mi><mi>A</mi><mi>B</mi><mo> </mo></math> có:</p>
<p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mi>O</mi><mi>A</mi><mo>'</mo></mrow><mrow><mi>O</mi><mi>A</mi></mrow></mfrac><mo>=</mo><mfrac><mrow><mi>O</mi><mi>B</mi><mo>'</mo></mrow><mrow><mi>O</mi><mi>B</mi></mrow></mfrac><mo> </mo><mo>⇒</mo><mfrac><mrow><mi>O</mi><mi>A</mi><mo>'</mo></mrow><mrow><mi>O</mi><mi>A</mi></mrow></mfrac><mo>=</mo><mfrac><mrow><mi>O</mi><mi>B</mi><mo>'</mo></mrow><mrow><mi>O</mi><mi>B</mi><mo>'</mo><mo> </mo><mo>+</mo><mo> </mo><mi>B</mi><mo>'</mo><mi>B</mi></mrow></mfrac><mo>=</mo><mfrac><mrow><mn>1</mn><mo>,</mo><mn>5</mn><mi>B</mi><mi>B</mi><mo>'</mo></mrow><mrow><mn>1</mn><mo>,</mo><mn>5</mn><mi>B</mi><mi>B</mi><mo>'</mo><mo>+</mo><mi>B</mi><mo>'</mo><mi>B</mi></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mn>3</mn><mn>5</mn></mfrac></math></p>
<p><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span> <math xmlns="http://www.w3.org/1998/Math/MathML"><mo>⇒</mo><mi>O</mi><mi>A</mi><mo>'</mo><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mn>3</mn><mi>O</mi><mi>A</mi></mrow><mn>5</mn></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mn>3</mn><mo>.</mo><mn>8</mn></mrow><mn>5</mn></mfrac><mo> </mo><mo>=</mo><mo> </mo><mn>4</mn><mo>,</mo><mn>8</mn><mo> </mo><mo>(</mo><mi>c</mi><mi>m</mi><mo>)</mo></math></p>
<p><math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mrow><mi>O</mi><mi>A</mi><mo>'</mo></mrow><mrow><mi>O</mi><mi>A</mi></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mi>A</mi><mo>'</mo><mi>B</mi><mo>'</mo></mrow><mrow><mi>A</mi><mi>B</mi></mrow></mfrac><mo> </mo><mo>⇒</mo><mi>A</mi><mo>'</mo><mi>B</mi><mo>'</mo><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mi>O</mi><mi>A</mi><mo>'</mo><mo>.</mo><mi>A</mi><mi>B</mi></mrow><mrow><mi>O</mi><mi>A</mi></mrow></mfrac><mo> </mo><mo>=</mo><mo> </mo><mfrac><mrow><mn>4</mn><mo>,</mo><mn>8</mn><mo>.</mo><mn>0</mn><mo>,</mo><mn>6</mn></mrow><mn>8</mn></mfrac><mo> </mo><mo>=</mo><mo> </mo><mn>0</mn><mo>,</mo><mn>36</mn><mo> </mo><mo>(</mo><mi>c</mi><mi>m</mi><mo>)</mo></math></p>
<p>đáp số: OA' = d' = 4,8cm</p>
<p><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span><span class="mce-nbsp-wrap" contenteditable="false"> </span> A'B' = h' = 0,36cm</p>
<p> </p>
<p> </p>
Hướng dẫn giải Câu C7 (Trang 123, SGK Vật lý 9)
GV: 
GV colearn
GV colearn
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Hướng dẫn giải Câu C7 (Trang 123, SGK Vật lý 9)
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