20. A single-slit of width a is illuminated by a light of wavelength. For what value of a will the first minimum appear at \( \theta \)? (A)\( \frac{1}{2}\lambda\sin\theta \) (B)\( \lambda\sin\theta \) (C)\( \frac{\lambda}{2\sin\theta} \) (D)\( \frac{\lambda}{\sin\theta} \) (E)\( \frac{3\lambda}{2\sin\theta} \)

1. Four particles are moving on a plane under the same constant acceleration \( \vec{a} = \hat{y} \), each having its initial velocity vector as follows: (a)\( 10\hat{x}+10\hat{y} \), (b)\( 10\hat{x}+8\hat{y} \), (c)\( 8\hat{x}+10\hat{y} \), (d)\( 12\hat{x}+12\hat{y} \). If the respective displacements are \( R_a \), \( R_b \), \( R_c \), \( R_d \), which of the following is correct? (A)\( R_a ＞ R_b ＞ R_c ＞ R_d \) (B)\( R_c ＞ R_b ＞ R_d ＞ R_a \) (C)\( R_d ＞ R_a ＞ R_b ＞ R_c \) (D)\( R_d ＞ R_a ＞ R_c ＞ R_b \) (E)\( R_a ＞ R_c ＞ R_b ＞ R_d \)

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