ANS:C - higher, as it gives shorter wavelength.

In X-ray radiography, the tube voltage for thicker plates compared to thin plates should be higher, as it gives shorter wavelength. This is because shorter wavelengths of X-rays can penetrate denser materials more effectively. Thicker plates require X-rays with higher energy levels (shorter wavelengths) to penetrate through them and produce clearer images. Conversely, lower tube voltages (higher wavelength X-rays) are sufficient for thinner plates as they require less penetrating power. Therefore, higher tube voltages are needed for thicker plates to ensure adequate penetration and image quality.