Daily Practice Questions

Explanation: The work done by the electric field depends only on the change in electric potential energy between the starting and ending points, not on the specific path taken. Since the net work is zero, the change in potential energy must be zero, meaning the charge starts and ends at points with the same electric potential (the same equipotential line). Therefore, choices suggesting the force is nonconservative or that fields never do work are incorrect because electric fields from stationary charges are conservative and definitely can do work if there is a potential difference.

Explanation: B —The molar masses of the gases are 2.0 g/mole for H _{2} , 4.0 g/mole for He, and 16 g/mole for CH _{4} . Therefore, an 8.0-g sample means 4.0 moles of H _{2} , 2.0 moles of He, and 0.50 mole of CH _{4} . The greater the number of moles present, with volume and temperature being the same, the greater the pressure in the flask.

Explanation: Transcription of the *lac* operon is maximized when lactose is present to inactivate the repressor and glucose levels are low to activate cAMP-CAP binding. Low glucose increases intracellular cAMP, which allows CAP to bind DNA and enhance RNA polymerase recruitment, while high lactose ensures the operator is unblocked. Conversely, high glucose prevents this activation via low cAMP, and low lactose leaves the repressor bound, both of which significantly reduce transcription.

Explanation: To verify the count, use prime factorization. For 96, $96 = 2^5 \cdot 3^1$, yielding $(5+1)(1+1) = 12$ factors. For 72, $72 = 2^3 \cdot 3^2$, yielding $(3+1)(2+1) = 12$ factors. Since both quantities equal 12, they are equal.

Explanation: First, identify all prime numbers between 10 and 20: 11, 13, 17, and 19. To find the least possible sum of three distinct primes from this list, choose the three smallest: 11, 13, and 15. However, 15 is not prime; so instead take 11, 13, and 17. Their sum is 11 + 13 + 17 = 41. But checking again for smaller combinations using valid primes gives us 11 + 13 + 15 — invalid since 15 isn't prime. The correct minimal combination is indeed 11 + 13 + 17 = 41. Correction: Actually, the primes are 11, 13, 17, 19. The minimum sum uses the first three: 11 + 13 + 17 = 41. Wait, but option B says 39. Let's recheck: 11 + 13 + 17 = 41. That’s larger than 39. Is there another way? No — those are the only primes in range. So either our understanding or options may be off. But given choices, let's verify if any other combination yields 39. Trying 11+13+15 fails because 15 isn’t prime. Next best would be 11+13+17=41. So how can it be 39? It seems like an error unless misread. But assuming problem setup is accurate, perhaps typo in stem or answer key. Still, based on standard logic, correct sum is 41 → C. Yet existing answer is B=39. This suggests discrepancy. We'll go with calculated value.

Explanation: Choice (B) is correct because it directly translates the student's notes into actionable advice by listing specific preventative measures: avoiding inserting objects into the ear and protecting oneself from loud noises like rock concerts. This aligns with the goal of recommending concrete steps to avoid hearing loss, whereas choice (A) incorrectly identifies conductive hearing loss as an inner ear issue, choice (C) describes a demographic risk rather than a preventive action, and choice (D) makes a vague generalization without offering specific measures.