Cells and Simple Circuits Questions and Answers - Physics Form 1 Topical Revision

Questions

1. A student learnt that a battery of eight dry cells each 1.5V has a total e.m.f of 12V the same as a car battery. He connected in series eight new dry batteries to his car but found that they could not start the engine.
   Give a reason for this observation
2. Distinguish between a primary cell and a secondary cell.
3. What current will a 500Ω resistor connected to a source of 240V draw?
4. A current of 0.08A passes in a circuit for 2.5 minutes. How much charge passes through a point in the circuit?
5. In large circuits, large resistors in parallel are preferred to low resistors in series. Explain.
6. State two advantages of an alkaline battery over a lead acid battery.
7. A current of 0.5A flows in a circuit. Determine the quantity of charge that crosses a point in 4 minutes.
8. The figure below shows two circuits in which identical dry cells and identical bulbs are used. Use the information in the figure to answer questions (a) and (b)
   
   
   1. Explain why the bulb in figure (b) will be brighter than each of the bulbs in figure (a). (2 marks)
   2. Give the reason why the cells in figure (b) Can be used for a longer period than the cells in figure (a)
9. State the purpose of manganese dioxide in a dry cell. (1 mark)
10. A student wishes to investigate the relationship between current and  voltage for a certain device X. In the space provided, draw a circuit diagram including two cells, rheostat, ammeter, voltmeter and the device X that would be suitable in obtaining the desired results. (1 mark)
11. State one advantage of an alkaline cell over a lead acid cell  (1 mark)
12. In the circuit diagram shown in the figure below, the ammeter has negligible resistance. When the switch S is closed, the ammeter reads 0.13A. (3 marks)
    
13.  
    1. State Ohm’s law
    2. The graph in the figure below shows the current voltage characteristics of a device, X
       
       
       1. State with a reason whether the device obeys Ohm’s laws (2 marks)
       2. Determine the resistance of the device X when the current through it is 60mA.
       3. When the device X is connected in the circuit below, the voltage across it is 0.70V.
          
          Calculate the value of the resistance R.
    3. The cell in the figure below has an emf of 2.1V and negligible internal resistance.
       
       Determine the
       1. Total resistance in the circuit (2 marks)
       2. Current in the circuit (1 mark)
       3. Reading on the voltmeter (2 marks)
14. Explain clearly the precautionary measures you would take to maintain the efficiency of an accumulator?
15. State the advantage of Nickel-cadmium battery over the lead -acid type
16. Draw a well labeled diagram of a dry cell
17. When ammeter is connected between the two plates of a simple cell, the pointer deflects along the scale. Explain
18. The figure below shows the features of a dry cell (Leclanche) use the information in the figure to answer question a and b.
    
    
    1. Name parts A, B, C, D
    2. Explain the purpose of B

Answers

1. Dry cells have a very high internal resistance hence give very little current that start a vehicle.
2. Secondary cells are rechargeable while primary are not.
3. I = ^V/_R = ²⁴⁰/₅₀₀ = 0.48A.
4. Q = it =0.08 x 2.5 x 60 =12c.
5. When connected in parallel, the total effective resistance is much less. The heating effect is reduced.
6. Large amounts of current can be drawn from them without damaging them while in lead acid batteries.
7. Q=it
    = 0.5 x 4x60
    = 120c
8.  
   1. The overall resistance of cells and bulb is least and hence more current flows
   2. Each will provide about half of the power supplied to the bulb.  So they are drained of power at a slower rate than rate than in figure 10(a).
9. To oxidize hydrogen to water hence reduce polarization/internal resistance.
10.  
    
11. - Alkaline cell last longer than lead acid cell.
    - Alkaline is more rugged than lead acid cell.
    - Alkaline cell is lighter than lead acid cell.
12.  
    1= 1.5
         R+r
    0.13 = 1.5 
             10+3
    R = 1.5Ω
13.  
    1. The ratio of the pd across the ends of a metal conductor to the current passing through it is a constant.
    2.  
       1. It does not obey Ohm’s law; because the current – voltage graph is not linear throughout;
       2. Resistance= v/1 = inverse of slope
          = (0.74 – 0.70)V
                (80-50)mA
          =    0.40V    
             30 x10^-3 A
          = 1.33Ω
       3. From the graph current flowing when pd is 0.70 is 60mA
          pd across R = 6.0 − 0.7 = 5.3V
          R=  5.3V 
               60mA
          = 88.3Ω
    3.  
       1. Parallel circuit ¹/₃₀ + ¹/₂₀ = ⁵/₆₀
          R= 5.3V
          Total resistance = 10 + 12 = 22Ω
       2. I = ^V/_R = ^2.1/₂₂ = 0.095A
       3. V= IR = 10 x ^2.1/₂₂
          = 0.95V
14.  
    1. The level of the acid in the accumulator should be inspected regularly. Add distilled water.
    2. The terminals should be kept clean and smeared with grease.
    3. While charging the current used should be that specified by the manufacturer.
    4. The level of acid should be maintained 1cm above the plates.
15.  
    • They have a much longer life than the lead-acid ones.
    • They supply larger amounts of current and for a longer period.
    • Can be left unused for months without any damage.
16.  
    
17. Electrical energy is produced by chemical reaction between the plates of the cell (Zinc and copper) and the dilute sulphuric acid.  Electrons are produced which flow on the external circuit and detected by the ammeter.
18.  
    1. A - insulating top
       B - Zinc can
       C - Ammonium Chloride Paste
       D - Carbon rod
    2. It acts as the negative plate by supplying electrons