C. change length and direction
Explanation:
The density of the material in which the light wave is travelling affects the speed of the wave. Different materials have different densities and they effect differently light waves which travel through them. Light waves may change direction at the boundary between two transparent materials, depending on material density. Density also impacts the speed of light. The denser the material, the slower light travels through it. The wavelength also decreases as light travels through the denser medium.
 
        
             
        
        
        
Answer:
first one is b 2nd one is a 3rd is c and the 4th one is c also 
Explanation: have a nice day
 
        
                    
             
        
        
        
A is the answer I really don’t know the answer to that but if u can u can help me on my work
        
                    
             
        
        
        
Answer:
a) according to Faraday's law
, b) creating a faster movement, placing more turns on coil
Explanation:
a) The voltage is induced in the coil by the relative movement between it and the magnet, therefore according to Faraday's law
            E = - d (B A) / dt
In this case, the magnet is involved, so the value of the magnetic field varies with time, since the number of lines that pass through the loop changes with movement.
This voltage creates a current that charges the battery
b) There are several ways to increase the voltage
* creating a faster movement, can be done by the user
* placing more turns on the coil, must be done by the manufacturer