Step 1: Understanding the Concept
The de Broglie wavelength is \(\lambda = \dfrac{h}{p}\), where p is the momentum.
Step 2: Electron
With energy E, \(p = \sqrt{2mE}\), so \(\lambda_e = \dfrac{h}{\sqrt{2mE}}\).
Step 3: Photon
For a photon of energy E, \(p = \dfrac{E}{c}\), so \(\lambda_p = \dfrac{hc}{E}\).
Step 4: Ratio
\(\dfrac{\lambda_e}{\lambda_p} = \dfrac{h}{\sqrt{2mE}}\cdot\dfrac{E}{hc} = \dfrac{1}{c}\sqrt{\dfrac{E}{2m}}\), which is option (D).
Final Answer:
The ratio is (1/c) times the square root of E/2m.
\[ \boxed{\text{(D) }\dfrac{1}{c}\sqrt{\dfrac{E}{2m}}} \]