[FEAT] Add Thin Lens formula for ray optics

src/main/java/com/thealgorithms/physics/ThinLens.java

@@ -0,0 +1,74 @@
+package com.thealgorithms.physics;
+
+/**
+ * Implements the Thin Lens Formula used in ray optics:
+ *
+ * <pre>
+ *     1/f = 1/v + 1/u
+ * </pre>
+ *
+ * where:
+ * <ul>
+ *   <li>f = focal length</li>
+ *   <li>u = object distance</li>
+ *   <li>v = image distance</li>
+ * </ul>
+ *
+ * Uses the Cartesian sign convention.
+ *
+ * @see <a href="https://en.wikipedia.org/wiki/Thin_lens">Thin Lens</a>
+ */
+public final class ThinLens {
+
+    private ThinLens() {
+        throw new AssertionError("No instances.");
+    }
+
+    /**
+     * Computes the image distance using the thin lens formula.
+     *
+     * @param focalLength focal length of the lens (f)
+     * @param objectDistance object distance (u)
+     * @return image distance (v)
+     * @throws IllegalArgumentException if focal length or object distance is zero
+     */
+    public static double imageDistance(double focalLength, double objectDistance) {
+
+        if (focalLength == 0 || objectDistance == 0) {
+            throw new IllegalArgumentException("Focal length and object distance must be non-zero.");
+        }
+
+        return 1.0 / ((1.0 / focalLength) - (1.0 / objectDistance));
+    }
+
+    /**
+     * Computes magnification of the image.
+     *
+     * <pre>
+     *     m = v / u
+     * </pre>
+     *
+     * @param imageDistance image distance (v)
+     * @param objectDistance object distance (u)
+     * @return magnification
+     * @throws IllegalArgumentException if object distance is zero
+     */
+    public static double magnification(double imageDistance, double objectDistance) {
+
+        if (objectDistance == 0) {
+            throw new IllegalArgumentException("Object distance must be non-zero.");
+        }
+
+        return imageDistance / objectDistance;
+    }
+
+    /**
+     * Determines whether the image formed is real or virtual.
+     *
+     * @param imageDistance image distance (v)
+     * @return {@code true} if image is real, {@code false} if virtual
+     */
+    public static boolean isRealImage(double imageDistance) {
+        return imageDistance > 0;
+    }
+}

src/test/java/com/thealgorithms/physics/ThinLensTest.java

@@ -0,0 +1,19 @@
+package com.thealgorithms.physics;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+class ThinLensTest {
+
+    @Test
+    void testConvexLensRealImage() {
+        double v = ThinLens.imageDistance(10, 20);
+        assertEquals(20, v, 1e-6);
+    }
+
+    @Test
+    void testMagnification() {
+        assertEquals(2.0, ThinLens.magnification(20, 10), 1e-6);
+    }
+}