GRE Subject 2026 Practice Test Physics Electromagnetism Free Quiz 2

11. What is the magnetic field of a long straight wire?

A. B = μ₀I/(4πr) B. B = μ₀I/(2πr) C. B = μ₀I/(2r) D. B = μ₀I/r

12. What is the magnetic field at the center of a circular loop?

A. B = μ₀I/(2R) B. B = μ₀I/(4R) C. B = μ₀I/R D. B = μ₀I/(2πR)

13. What law states that the induced current opposes the change?

A. Faraday B. Ampere C. Gauss D. Lenz

14. What device stores electric field energy?

A. Inductor B. Capacitor C. Resistor D. Diode

15. What device stores magnetic field energy?

A. Inductor B. Capacitor C. Resistor D. Diode

16. What is the energy stored in an inductor?

A. ½CV² B. ½QV C. ½Q²/C D. ½LI²

17. What is the Poynting vector?

A. S = (1/μ₀)(E × B) B. S = E × B C. S = E·B D. S = B × E

18. What is the relationship between E and B in an electromagnetic wave?

A. Parallel B. Anti-parallel C. Perpendicular D. Arbitrary

19. What is the impedance of free space?

A. 50 Ω B. 75 Ω C. 100 Ω D. 377 Ω

20. What is the skin depth?

A. Wavelength B. Skin depth C. Penetration depth D. Attenuation length