1 Republic of the Philippines Department of Education Region VII, Central Visayas DIVISION OF MANDAUE CITY MANDAUE CITY COMPREHENSIVE NATIONAL HIGH SCHOOL Instruction: Read Chapters 23 until 32 of the resource material “Introduction to Biological Physics for the Health and Life Sciences” by Franklin, et al., and answer the following questions below. Use a separate sheet of paper and illustration if necessary. 23.1 An uncharged metal sphere, A, is on an insulated base. A second sphere, B, of the same shape, size and material carrying a charge +Q is brought into contact with sphere A. (a) Describe what happens to charges on spheres A and B as they are brought into contact. (b) If we now remove sphere B and place it far away, what is the charge on sphere A? (c) How is this charge (if any) distributed? 24.1 A +3×10−6 coulomb charge is placed 5 centimetres due west from a +2×10−6 coulomb charge. (a) What is the force the +2 μC charge exerts on the +3 μC charge? (b) What is the force the +3 μC charge exerts on the +2 μC charge? 25.1 A 20 000 NC−1 uniform electric field does +5 000 J of work on a +0.20 C charged object. (a) Did the charged object move in the direction of the electric field or against it? (b) How far did the object move? (c) What was the change in electrical potential through which the object moved? (d) If the object was initially at a point with an electrical potential of −2000 V, what was the electrical potential its end point? 26.1 A 9 V battery is connected to a capacitor which subsequently has a magnitude of 0.5 μC of charge on each plate, with the charge on each plate having an opposite sign. What is the capacitance of this capacitor? 27.1 Sodium ions (Na+) are flowing through a cylindrical ion channel which has a diameter of 0.85 μm and is 5 μm long. There is a potential difference of 225 mV between the ends of the channel. The sodium ions have a drift velocity through the channel of 0.015ms−1 and in a period of 1 ms a total of 15×106 ions exit the channel. (a) What total charge exits the channel in a time period of 1 ms? (b) What is the current in the ion channel? 2 (c) What is the ‘resistance’ of the channel to the flow of sodium ions? (d) What is the number density, n, of ions in the channel? (e) How many sodium ions are in the channel at any one time? 28.1 An 18 μF capacitor has been charged to 100 V. A 15 kΩ resistor and a 5 kΩ resistor, are connected in series with the capacitor. (a) What is the time constant of this circuit? (b) Approximately how long (in terms of τ) will it take for the charge stored on the resistor to drop to 0.1% of its original charge? Once the capacitor is fully discharged the 5 kΩ resistor is removed and replaced with a 12 V battery. (c) What is the time constant of the circuit now? (d) Approximately how long will it take for the charge stored on the resistor to rise to 95% of its maximum charge (in terms of τ)? 29.2 It is not possible to make images of, and therefore see, arbitrarily small objects using visible light. The minimum size of an object that can be ‘seen’ by light using conventional optics is roughly equal to a few times the wavelength of the light used. If a bacterium that is 1.2 μm across can just be seen using a particular optical system when the bacteria is floating in a watery solution (nsolution = 1.35), what will be the minimum size of bacterium that this optical system could ‘see’ in air (nair = 1.0)? 30.2 Is it possible for a diverging lens to form a real image of a physical object? If so, under what conditions is the image real? If not, why not? 31.2 A person with a normal lens-to-retina distance wears contact lenses with an optical power of 1.2D in order to be able to clearly see objects 25 cm in front of them. (a) What kind of vision defect does this person have? (b) What is this person’s near point (without the contact lenses)? 32.2 A high intensity source of microwaves used in a piece of medical diagnostic equipment is not adequately shielded. The microwaves produced by this equipment have a frequency of 150 GHz, and there is a gap in the shielding 1 cm wide. At what angles from the gap in shielding will the intensity of the microwave radiation be zero? (Assume the microwaves are incident normally to the gap.)
