Three charges are arranged as shown in Fig below Find the force on the charge Q3 assuming that. Q1 is -9.0 10⁻¹⁰ C, Q2 is 3 10⁻¹⁰ C and Q3 is -6 * 10⁻¹⁰ C and Q1 and Q3 are 2.0 m from Q2. /3marks

Since $Q_1$ and $Q_3$ are both negative, they repel each other. The force $F_{13}$ on $Q_3$ is directed to the right.

$$F_{13} = k \frac{|Q_1 Q_3|}{r_{13}^2}$$ $$F_{13} = (8.99 \times 10^9 \text{ N m}^2 \text{ C}^{-2}) \frac{|(-9.0 \times 10^{-6} \text{ C})(-6.0 \times 10^{-6} \text{ C})|}{(4.0 \text{ m})^2}$$ $$F_{13} = (8.99 \times 10^9) \frac{54.0 \times 10^{-12}}{16.0}$$ $$F_{13} = 0.03034125 \text{ N}$$

Since $Q_2$ is positive and $Q_3$ is negative, they attract each other. The force $F_{23}$ on $Q_3$ is directed to the left.

$$F_{23} = k \frac{|Q_2 Q_3|}{r_{23}^2}$$ $$F_{23} = (8.99 \times 10^9 \text{ N m}^2 \text{ C}^{-2}) \frac{|(3.0 \times 10^{-6} \text{ C})(-6.0 \times 10^{-6} \text{ C})|}{(2.0 \text{ m})^2}$$ $$F_{23} = (8.99 \times 10^9) \frac{18.0 \times 10^{-12}}{4.0}$$ $$F_{23} = 0.040455 \text{ N}$$

Let the direction to the right be positive.

$$F_{net} = F_{13} - F_{23}$$ $$F_{net} = 0.03034125 \text{ N} - 0.040455 \text{ N}$$ $$F_{net} = -0.01011375 \text{ N}$$

The negative sign indicates the net force is directed to the left.
The net force on $Q_3$ is $\boxed{\text{0.010 N to the left}}$.

physical properties that affect resistance of a metal wire. /3 marks
The physical properties that affect the resistance of a metal wire are:

• The length of the wire: Resistance is directly proportional to length.
• The cross-sectional area of the wire: Resistance is inversely proportional to the cross-sectional area.
• The type of material (resistivity): Different materials have different inherent resistivities.
• The temperature of the wire: For most metals, resistance increases with temperature.

graph of current against p.d for the following; /1 mark

• For a resistor, the graph of current (I) against potential difference (p.d or V) is a straight line passing through the origin, indicating a constant resistance (Ohm's Law).
• For a diode, the graph is non-linear. It shows very little current flow in reverse bias, and in forward bias, current only starts to flow significantly after a certain threshold voltage (cut-in voltage) is reached, then increases exponentially.

e.m.f 3.0 V and negligible internal resistance is connected across three re... as shown in figure
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